Gunshot Residue Analysis Webinar Series Transcripts

Webinar #1 – “Sample Collection and Submission”
Webinar #2 – “Analysis and Testimony Considerations”

Webinar #1 – “Sample Collection and Submission”

To download a PDF of the webinar, please click here.

Presenters: Allison Murtha, Michael Gorski, Marsha Hess

Date: February 25, 2015

Allison Murtha – Narrator

Slide 1
Good afternoon, everyone. My name is Allison Murtha and I’m a manager and forensic scientist at RJ Lee Group in the Forensics Department. Welcome to Day #1 of our webinar series, “Gunshot Residue Analysis for Law Enforcement.” Today’s series will include sample collection and sample submission. Day #2 of our webinar series will be about sample analysis and some testimony considerations. There’s still room in our Day #2 webinar series, so feel free to sign up, and we’ll be looking forward to seeing you there, as well.

I’d like to introduce you to the two individuals you’ll be hearing from today. You’ll be hearing from Mr. Michael Gorski about sample collection. He’s a forensic scientist in the forensic science department. You’ll also be hearing from Mrs. Marsha Hess, our project coordinator in the forensic science department. She’ll be talking about sample submission. Without further ado, I’m going to turn it over to Mr. Michael Gorski. Mike?

Michael Gorski – Presenter

Slide 2
Good morning! Today I’m going to talk to you a little bit about gunshot residue sample collection. We’re going to discuss WHO you want to sample from, WHEN you want to sample, WHERE you want to sample, and also considerations to take into account when sampling.

Before we get into sample collection, I want to briefly touch on what gunshot residue, or GSR, is. Gunshot residue is the material that comes out of a firearm whenever it is discharged. This material includes elements from the gun primer, the gun powder, and also the firearm and ammunition itself. The portion of material that we are going to focus on today, the material that can link particles to a firearm’s discharge, originates from the primer.

The primer typically contains three elements that are highly specific to the discharge of a firearm whenever all three of those elements are found together in one particle. Those elements are lead, antimony, and barium. When a firearm is discharged, those elements originating from the primer can land on the hands, clothing, and surrounding area of the shooter. To hear a little more about the GSR particulate as well as testimony considerations, tune into Day #2 of our webinar series.

Now let’s talk about collecting those particles that may have landed on the hands, clothing and surrounding areas of a potential shooter.

Slide 3
When collecting samples for GSR analysis, the ONLY type of kits that should be used are SEM, or Scanning Electron Microscopy, kits. These kits are the industry standard.

GSR hand and surface kits can be purchased from a variety of different manufactures, including TriTech, Sirchie, and Arrowhead, as well as RJ Lee Group.

The samples in the kit are what we refer to as a “stub.” A stub is an aluminum pin mount encapsulated in a plastic vial. The pin mount has an adhesive material on it that is used for the actual collection. Kits can contain anywhere from 2-5 sample stubs. Some kits only have stubs for the right hand and left hand, and others like RJ Lee Group’s have five: stubs for the right back, right palm, left back, left palm, and control. It is up to you and your agency as to what kind of kit to purchase.

If you are ever in a pinch and do not have access to a GSR SEM kit, do NOT use a Q-tip or swab. At the very least, use a small piece of packing tape. However, if you have clothing or another item in-house for collection, and are in need of a kit, give us a call and we’ll get you one quickly.

Slide 4
GSR samples can be collected from a suspected shooter’s hands or face area using those SEM stubs. At times, we do receive samples from victims’ hands as well, and we can analyze them if you deem them probative to the case. However, it would not be very unusual to see GSR on a victim of a gunshot wound. So typically the samples we receive are from suspected shooters.

Samples can also be collected from a subject’s clothing or other item relating to the subject. This is sometimes a more probative path to take, especially if it has been several hours or days after a shooting incident. GSR particles may tend to adhere longer to clothing than to the skin of a shooter. This is because the particles can get trapped into the weave of the fabrics that the clothing is made out of. Typically, an individual is going to have washed himself or herself more often than they would have washed their clothing.

Vehicles can also be a good source to collect GSR from if you suspect a firearm has been discharged from within the vehicle.

Items that can be analyzed include samples from hands, vehicles, all types of clothing, cell phones, helmets, sunglasses, purses, and jewelry, just to name a few.

Use your best judgment. What item do you feel is most likely to retain the most GSR after a certain amount of time has elapsed? And as always, if you have questions, call us!

Slide 5
We frequently get asked on the stand WHEN you should collect samples for gunshot residue. The simplest answer to this question is to collect them AS SOON AS POSSIBLE after the incident.

There are some labs out there that have what are called “cutoff times.” For example, if a suspected shooter isn’t apprehended and samples aren’t collected before a certain hourly timeframe of a shooting incident, some labs will not accept the samples for analysis. This is because there are several factors (running, weather, activity etc.) which can cause particulate loss.

RJ Lee Group does NOT utilize a cutoff time, believing instead to follow what the investigating officers feel are instructions of probative value. If you collect samples from a suspect’s hands three days after a shooting, we will analyze them for you if that’s what you want us to do, but the chances of still finding particulate are unlikely. Three days after a shooting, the probative value of collecting samples from an individual’s hands decreases tremendously. It’s cases like that when you want to look into taking samples from a subject’s clothing, or other items worn during the time of a shooting.

We frequently get asked on the stand when you should collect GSR samples. Collection should be performed as soon as possible (at the scene whenever possible!)

This is important because of particle loss. The more time passes, the more activity occurs. Activity is a major factor for particle loss on a surface, such as washing, wiping, running/movement, perspiration, etc.

Slide 6
Now we’re going to go over “where.” Where should you collect the samples? If you should collect samples as soon as possible, that typically means that you will be collecting samples at the scene.

By collecting samples at the scene, there are fewer opportunities for contamination to be introduced and fewer chances for movement or activity of a subject over time.

However, we do realize that it is not always possible to collect samples at the scene. When you cannot collect at the scene, it is very important to bag the subject’s hands. A brown paper bag over each hand of the subject will protect any possible contamination that could originate from a police officer’s handcuffs, or contamination that could originate from the back seat of a police vehicle.

Whether collecting samples from the hands of a subject or bagging a subject before handcuffing him or her, we always recommend wearing latex gloves, and please do so. A pair of latex gloves serves to protect from any potential transfer of particles from you to the subject. They also serve to protect you in court when you are questioned about best practices when collecting samples.

Slide 7
Now I’m going to go over some considerations to think about choosing when to actually sample and collect. There are many things to consider when collecting samples for gunshot residue.

There are certain factors which can contribute to particulate loss. These factors can play a role in whether or not samples will have probative value for analysis.

  • Movement, motion, and activity are big factors which could cause particulate loss, and the more time that passes, the more potential there is for particulate or particles to be lost. Washing hands, wiping hands on clothing, putting hands in and out of pockets, running, shaking hands with other people … these are all activities that could cause particles to be removed. This is also why clothing may be a better option for you to consider sampling, if a long amount of time has passed since the incident.
  • It may also be important to note a subject’s activities prior to the incident, as well. For example, if a subject states that on the morning of the incident he or she went to the gun range or that they went hunting, then finding GSR on him or her wouldn’t be unusual. At that point, GSR analysis may not be very useful to you.
  • Weather and airflow might affect the number of particles detected on a suspected shooter. When shooting incidents occur outside, wind, rain, snow, or humidity could also wash away particles or affect the amount of particles that land on the shooter. Shooting incidents that occur inside can be affected by air movement in the room. Fans, air conditioners, or even having the windows open may affect particulate loss or the number or particles deposited.
  • Blood and other biological material can act as a “mask” for particles that are on a subject’s hands or clothing, making them not readily able to be collected. When collecting samples, it is important to try to sample around areas that have a lot of biological material present.

Contamination from other sources is another issue to consider when collecting samples. Officers collecting from subjects need to be especially cautious, as they and their surroundings can contain GSR. As mentioned previously, wear gloves and be aware of potential contamination sources around a collection area. If possible, have an unarmed officer collect the samples.

It is not uncommon to find only one or a few GSR particles on a case sample, and you do not want to be a possible source of these particles.

As I stated previously, if collection cannot be done at the scene, it is highly recommended that the subject’s hands be bagged before being cuffed. This is done to prevent any contamination from getting onto the subject’s hands. If you will be collecting samples at your agency, then be sure to wear gloves, ensure a CLEAN environment (for example, don’t collect samples in the ballistics unit), and clean surfaces before subject is brought in for sampling. Be sure to lay out paper, do things that will prevent contamination.

We also want you to consider packaging. When you are packaging clothing to be sent for sample collection, the items should be packaged individually so no cross-contamination occurs. Each article of clothing can be wrapped in butcher paper and placed in separate evidence bags.

Slide 8
Now let’s take a closer look at a gunshot residue hand kit. This particular hand kit contains five stubs: stubs for the back and palm of the right hand, and for the back and palm of the left hand, as well as a control.

When using the “right back” or “right palm” stub, that should correspond to the subject’s right hand. The “left back” or “left palm” stubs should correspond to the subject’s left hand.

The control stub is a stub that can be utilized however you see fit. It can be used to sample the area or room in which the samples are being collected to prove that it is free of GSR particles, or it can be used to sample the hands of the individual doing the collecting. Some agencies choose to use the control stub as a “batch control,” to prove that there is nothing present on the stubs before they are used to sample. The use of a control stub is completely and totally up to you, but using them DOES help to bolster credibility in the courtroom.

The first step is to prepare yourself before you collect samples. Take note in the picture, that the individual doing the collection is wearing appropriate personal protective equipment with latex gloves while doing the containment.

Slide 9
Now I’m going to go over how to actually sample from a suspect’s hand. This image would be representative of the back right hand of the shooter.

The method used to sample areas of interest is called “particle extraction.” It’s basically a dabbing motion.

First, you want to remove the cap from the stub. Then you place the stub face down on the area of interest. In this picture, we are seeing the “right back” of a hand, and every circle indicates one “dab.”

When sampling hands, you want to focus first on the area that usually has the greatest concentration of particles: the area and webbing between the individual’s thumb and forefinger. Once that is complete, you want to start dabbing up and down the hand in a vertical motion, ensuring to cover the entire hand.
Be sure when you dab that you put the stub down and then bring it right back up. Please do not drag the stub along surface of the skin. That could cause the adhesive to curl up on itself, degrade, or possibly mask particles that are being preserved. These blue dots represent the vertical motion of dabbing over the suspect’s hands.

Once you have dabbed over the hand in a vertical direction, you want to dab over the hand in a horizontal direction, and that’s what’s going to be represented by these black dots. This will create a grid-like pattern over the hand, ensuring that the entire hand has been sampled.

Slide 10
Now I’m going to go over sample collection from, let’s say, an article of clothing. When sampling clothing or other items, the same method of particle extraction is used. The dabbing technique is applied in vertical and horizontal directions creating a grid-like pattern over the area of interest.
When samples are taken from clothing, typically more than one sample is needed. This is because the adhesive properties of the stub will wear off over time and in the amount of area being sampled.

As an example, when collecting samples from a long sleeved shirt, sweater, or jacket as shown in the picture, we would use four stubs to sample the item – one for the right sleeve, one for the right side, one for the left side, and one for the left sleeve. This ensures the entire area of the sweater would be sampled.

Other areas of clothing can be sampled based upon what YOU feel is of probative value. For example, it is possible to particle extract from pockets or waistbands if you believe that a recently discharged firearm may have been holstered in those areas. It really is up to you.

Particle extraction of clothing and other items, like purses, phones, sunglasses, can be sampled at your agency, given that you have an appropriate area and clean room to use. Or, if you don’t feel that you have a clean, contamination-free area, they can be sent to a lab like RJ Lee Group for sample collection, followed by analysis.

Slide 11
Now I’m going to go over sample collection from vehicles. Vehicles are another common area for GSR samples to be collected from, depending on the nature of the case at hand.

The same method of particle extraction is utilized on the vehicle as is utilized on hands and clothing. Potential areas to sample from include, but are not limited to, seats, headliners, door paneling, consoles, dashboards, steering wheel , the list goes on.

When sampling from a vehicle, consider the flow of an incident before collecting. For example, if a potential shooter fired a gun out of the driver’s side window, you would want to collect samples from the driver’s door before you collected samples from the passenger seat or rear passenger seat.

Another thing to consider is the material of the surface that you are sampling from. Particles are going to tend to adhere better to fabrics vs. vinyl, plastic, or metal on the outside of the vehicle.
If at any time during the investigation of a case you have a question about what areas may or may not be probative, please feel free to give us a call! We can always aid in helping you determine whether or not collecting samples for GSR is a viable option for you and your particular situation.

Slide 12
Now I’m going to go over why correct sampling is incredibly important. In an ideal world, every sample that you collect would have hundreds to thousands of GSR particles on them. Well, that’s possible. They could, and we HAVE seen samples that have hundreds of particles on them.

However, let’s be realistic. We tend to see samples with a few particles on them, or ONE particle on them, or no particles on them at all. This is because of all the factors that we went over previously: weather, action/activity, time, washing, etc. Because of these factors, you want to make sure that you are collecting any and all potential particles that could be present to be collected. Therefore, we want to make sure that you are sampling correctly and efficiently.

By sampling properly, not only are you ensuring that you are collecting any and all particles present, but you are also ensuring an easier time testifying. You can say, under oath, that you have sampled correctly and appropriately based on the standard set forth in the field.

Slide 13
Now I’m going to go over some packaging considerations. Once samples are collected and ready to be sent off for analysis, you’ll need to be sure that they are packaged properly.

Proper packaging is one way that possible contamination can be controlled. GSR hand kits typically are sent in an evidence bag with samples, latex gloves, and seals. After collection, the samples should be placed in the evidence bag and sealed with tape.

When packaging clothing, items should be packaged in butcher paper before packaging. When multiple items are contained in one bag, cross contamination can occur; therefore, only one item should be placed in a bag. This is important, especially if you have items coming from multiple people. Please do not place multiple bags from multiple people in one bag. The bags should then be sealed completely, with no rips or voids. Evidence tape should be used with your initials and date on the seal of the package. Please DO NOT USE staples. We will photo and document this, and it may come up during discovery.

Once the samples are packaged, they are ready for shipping, and Marsha is going to talk to you a little bit about our portion of analysis.

Marsha Hess – Presenter

Slide 14
Hello, everyone. My name’s Marsha Hess and I am the project coordinator in the Forensics Department. If you call RJ Lee Group and ask to speak to someone in the Forensic Group, I will probably be the one to take the call. Some of my other responsibilities include logging evidence into our database upon processing, as well as scheduling our experts for trial testimony, conference calls and depositions. Today, I’m going to go over the proper procedures for submitting evidence to our laboratory for analysis.

Slide 15
As Mike stated, all evidence should be properly packaged and sealed. A chain of custody or a submission letter should be included with the evidence.

Slide 16
Let’s talk about the Chain of Custody. If your agency has a Chain of Custody, please enclose it with the evidence. If you need to obtain a COC, you can download one from our website. You can go to, and click on submit a sample. From there you will see 3 options:
a General COC, IH/Environmental COC, and Vermiculite Analysis COC. For submission of forensic evidence, you want to choose the General COC.

Slide 17
This is what General COC from our website looks like. This form is self-explanatory. The fields you want to pay special attention to are the, “Report Results to,” “Send the Invoice to,” and the “Client Sample ID.” Please list the items you’re submitting, so we can verify what you sent is what we received.

Slide 18
If you prefer not to use our on-line form, we ask that you enclose a submission letter with the samples. Here is an example of a submission letter, and we first want to make sure that you submit it on your company’s letterhead. We also ask that you include the following information:

    • Type of analysis requested, such as gunshot residue analysis
    • The case number, which would be your police department or agency case number
    • A list of evidence submitted for analysis so we can verify what you sent is what we received

We would also like you to include a brief synopsis of the case, such as subject/victim names, right or left handed, etc. We ask for this because a lot of times we’ll do some case work and a year later, we’ll receive a subpoena for testimony. The subpoena number will be different than the agency case number. Without subject names, we can’t reference what case is going to trial, so it’s very helpful. The more information we have, the better the chances we can link everything up in case it comes up later for trial.

The next thing we ask is that you list the ”Report to” contact information, which would be name, address, phone number. If the billing information is different than the “Report to” contact, please list that. A lot of times we’ll get the evidence from the police department; however, it’s going to be billed to the District Attorney’s office, and that’s helpful so we can get it right the first time.

Slide 19
Evidence can be shipped through any means that provides that package with a tracking number, such as UPS, FedEx, USPS, or certified mail. Evidence can also be hand-delivered to RJ Lee Group’s office. We have a lot of local agencies that just come on in to drop their evidence off, and we’ll have Chain of Custody forms ready when you arrive. We can accept your evidence at that time.

Once we receive and process the samples, our standard turnaround time is 5-10 business days.
Upon completion of analysis, we send all samples back using UPS, unless otherwise instructed.

Slide 20
I’d like to thank you all for joining us today. I’m now going to turn it back over to Allison Murtha.

Allison Murtha
Thanks, Marsha. Again, thank you on behalf of the entire forensics department for tuning in today. We look forward to seeing you at Day 2 of our series. Thank you very much for your attention. Take care!

Webinar #2 – “Analysis and Testing Considerations”

To download a PDF of the webinar, please click here.

Presenters: Allison Murtha & Stephanie Horner

Date: March 11, 2015

Allison Murtha – Presenter

Slide 1
Good afternoon and thank you for joining us for Part Two of RJ Lee Group’s webinar series “Gunshot Residue for Law Enforcement.”

My name is Allison Murtha and I am the manager and a forensic scientist in the Forensics Department at RJ Lee Group. Today you will be hearing from myself, as well as Stephanie Horner, another forensic scientist at RJ Lee Group. Today we’re going to talk about the analysis of gunshot residue, as well as considerations when testifying to the evidence.

At the conclusion of this webinar, you’ll be receiving an email in about 2-3 days’ time, including a link where you will be able to view the webinar in its entirety.

Along with that link, you’ll also be able to see Day One of our webinar series. At the end of the webinar, there will be a brief question and answer, and we encourage you to ask questions. If at any time during the presentation you have a question, please feel free to use your question tool located on the panel on the right-hand side of your screen. We will get to as many of your questions as possible during the question period at the end of the presentation. If we are unable to get to your question, we will contact you after the webinar to be sure that your questions and/or concerns have been addressed.

Also, if you do need a certificate to show that you attended the presentation, you can request one by using the question box. Please include the name you’d like on the certificate, as well.

At this point, I’d like to turn it over to Stephanie Horner to talk about the scientific aspects of gunshot residue.

Stephanie Horner – Presenter

Slide 2
Last week Mr. Gorksi went over the collection of GSR. He covered the “who” and “what” and “how” of collections. I’m going to start by giving you a background on GSR. What exactly is GSR? How is it created?

Slide 3
In the broadest sense of the word. GSR is all particulate that is expelled from a firearm during discharge. For the purposes of this webinar, when I refer to gunshot residue, I am specifically talking about primer residue.

Slide 4
There are many components to gunshot residue. If you look at the picture of the cartridge on the right, you can see where all the particles that make up GSR originate from. At the very bottom, you have the primer cap. Inside the primer cap is the primer paste. The primer paste is typically composed of lead, antimony and barium. Those are the elements that we look for when we are looking for gunshot residue. It is important to note in the image that you are looking at a center fire primer cap. Depending on the cartridge, you could also see rim fire.

Next to the primer you can see the propellant or powder. The powder is composed of nitrogen based compounds including nirtrocellulose and nitroglycerine. These components are important when analyzing evidence for distance determination. While RJ Lee group can perform distance determination, I am not going to cover it in this webinar.

The bullet is next to the powder. It is what is forced out of the firearm during discharge. In addition to seeing elements from the primer and the powder in a population of GSR, we see some other metals from the ammunition and firearm. Aluminum or tin can come from a thin layer of tin or aluminum foil that is used to separate the primer and the powder.

Slide 5
Now you know where GSR particles come from, but how are they actually produced? When the trigger on a firearm is pulled, the firing pin will strike the back of the primer cap. This causes the primer residue to burn, which in turn ignites the gunpowder. The burning of the powder results in a lot of pressure and heat within the firearm. The pressure will force the bullet out of the firearm.

Slide 6
While this is happening all of those tiny particles from the primer and powder escape out of the firearm through any opening. They will come out the muzzle, ejector port, or any other opening in the firearm. As the elements cool, they condense and land in tiny particles on the shooter and the surrounding area. Those particles can be collected using an SEM stub as described in Day 1 of this webinar.

This image shows the cloud of particulate that is expelled from a firearm when discharged. The cloud is often referred to as the plume. Remember this plume includes particles from the primer, powder, and other miscellaneous metals from cartridge. In this plume there are hundreds or thousands of microscopic particles that will condense and fall on the hands of the shooter and surrounding area. The particulate coming from the plume is actually what you will be collecting.

Slide 7
From that plume, the particles that we are most concerned with are the primer particles. Let’s take a closer look at those particles. The plume is typically a high-temperature super saturated concentration of three important elements: lead, barium, and antimony. As the temperature cools, those elements are going to condense into different combinations, creating 1-2-3 component particles.

Three-component particles are what we refer to as “characteristic” of GSR. They are highly specific to the discharge of a firearm. Three component particles contain the elements of lead, antimony and barium. We must see all three of the elements in the same particle for that particle to be considered highly specific to GSR. In addition to the correct elements, we must also see the correct shape or morphology. The particles must be round or molten, as if they are heat treated, since the discharge of a firearm in a very high heat reaction. These are the particles that have to be present in order for a population to be considered GSR.

Two-component particles contain two of the three elements. So that would be a particle that contains lead and antimony OR lead and barium OR barium and antimony. Two-component particles are considered consistent with the discharge of a firearm.

One-component particles contain just one of the three elements. So a particle of just lead OR just barium OR just antimony. One component particles are considered commonly associated with the discharge of a firearm.
However, there are some brands or types of ammunition which could create different compositions. For example, some .22 Rimfire CAN lack antimony in the primer, or there are non-toxic ammunition which could be lead-free.

In addition to lead, barium and antimony, there are other elements which can be found in GSR but are not required. Some examples would be silica, copper, tin, and aluminum.

There are also elements that when seen with lead, barium or antimony that would cause us to eliminate that particle as coming from the discharge of a firearm. Some examples would be magnesium, chromium or titanium. The presence of these particles would let us know that is likely that particle came from some other source besides GSR. For example, particles containing magnesium can be found in fireworks.

Slide 8
Primer GSR particles are so small that they can’t be seen by the naked eye. This is why we need a high-powered microscope to view the particles. In this picture, you can see a human hair next to a GSR particle. You can fit 20 to 100 GSR particles across the width of a human hair.

Slide 9
This is an image showing a GSR primer particle taken using the scanning electron microscope. Here you can see the peaks representing each element. The lead peaks are labeled with Pb, the antimony peaks are labeled with Sbn and the Barium peaks are labeled with Ba. You can also see the elements of silica labeled as Si and tin labeled as Sn. It is possible to see both silica and tin in GSR.

Another important thing to look for is the shape of the particle. As you can see, this particle is round. GSR particles have a round and molten appearance due to the high heat reaction.

The image you are looking at is magnified using the SEM. The image on the left is magnified 400x and the image on the right is magnified 2000x. The particles need to be magnified thousands of time in order to be viewed since they are so small in size.

Slide 10
The scanning electron microscope, or SEM, is the most current and up-to-date method for GSR analysis. You can see from this image that the SEM is controlled by, and the particles are viewed on, a computer screen.

Slide 11
The SEM allows us to see GSR particles and analyze them. All GSR samples are analyzed using the SEM at RJ Lee Group. The samples are loaded into the microscope. A beam of electrons is aimed at the sample. The interaction of those electrons with sample electrons determines two things. The first thing is the elemental composition of the particle, or what that particle is actually made out of. The second thing is the shape of the particle.

The SEM has a two-part analysis. The samples are first analyzed using an automated analysis. The SEM scans back and forth across the surface of a sample looking at the elemental composition of all particles. The instrument marks the location of any particle of interest. The second part is a manual analysis. The analyst will look at the particles of interest that the SEM found and confirm that the instrument made the correct calls. The particles that are confirmed during the manual analysis are the particles that we report out.

The average analysis time using the SEM is 4-8 hours per sample. A case can take much longer to analyze, depending on how many particles are found on each sample and how many samples are in each case. If you have a typical hand kit with 5 stubs for analysis, this can take anywhere from 20 to 40 hours, or even longer.

Slide 12
There are some outdated methods for GSR analysis that I am going to touch briefly on. Most of the outdated methods for GSR analysis are actually testing for the powder residue and NOT the primer residue.

Some of the other tests for GSR are the paraffin or dermal nitrate test, Instant Shooter Identification test, or the Rapid Identification Friend or Foe test. These tests look for nitrogen-based compounds or powder residues. The ISID and RIFF tests can be used in the field and give instant results. However, these tests are presumptive and not confirmatory. These tests can result in false positives or false negatives. Some false positives include fertilizers, tobacco and certain foods. These tests are often marketed as tests for primer residue when they actually look for powder residue. The only analysis that is confirmatory is PRIMER analysis.

The atomic absorption test also looks for lead, antimony, and barium. However, it is a bulk analysis. This means that it can only determine whether the sample contains lead, barium, and antimony, but cannot tell if they are present together in one particle. The atomic absorption test does not look at individual particles, which is necessary to determine the presence of GSR.

Slide 13
There are many reasons that the SEM is used over other methods for GSR analysis.

The SEM is a confirmatory analysis. It is not a presumptive test like some other field tests used for GSR. The confirmatory test allows us to say whether or not primer GSR is present. The SEM can look for individual particles and can aid the scientist in determining if that particle came from the discharge of a firearm.

SEM kits are inexpensive and can be stored indefinitely. The kits do not expire and can be used whenever you need them.

SEM samples are fast and easy to collect, and sampling can easily be performed at the scene.

The SEM is a non-destructive technique. This means that the evidence itself is not destroyed during analysis. For example, GSR samples can be taken from a shirt and the shirt can still be sent for DNA analysis after the GSR sampling.

The samples can be analyzed as many times as you would like, getting the same results each time. It is easy to duplicate the analysis.

These are the reasons why we always recommend SEM analysis over other types of analysis. Not only because of the reasons I just listed, but it also holds up in court. Allison is going to go over some testimony considerations with you now.

Allison Murtha – Presenter

Slide 14
Thanks Steph!

Yes! Gunshot residue analysis via the scanning electron microscopy DOES hold up well in court – it is the standard and approved technique by experts in the field.

When testifying to GSR evidence, there are several considerations that it is important that you be aware of when submitting samples for analysis. There are certain things that we CAN say and certain things that we CAN’T say when testifying. Today we want to give you a little insight into how our testimony may be able to help your investigation.

Slide 15
A lot of the questions we get asked about in court revolve around “hypothetical situations.” Lawyers want to know and want to get this across to the jury: how much GSR to expect under certain circumstances or certain conditions. Situations like these are difficult to predict because of all of the different variables that come into play.

Really, the best way to answer a hypothetical question is by giving you some hypothetical scenarios. So that’s what we’re going to do today.

Let’s first take a look at an “IDEAL scenario.” This is a situation in which everything goes according the “Forensic Plan.” In other words, the stars are aligned and the world is a perfect place.

In this situation, the shooting takes place in what we call a “static environment.” What this means is whether or not the incident takes place indoors or outdoors; there is no airflow or precipitation. If it’s inside, there’s no air conditioning, there’s no fan, no air movement. If it’s outside, there is NO wind, rain, snow or any type of weather.

Let’s assume that the firearm functions properly and creates a lot of GSR when it is discharged.

Let’s also assume that samples are collected from the hands or clothing of the shooter IMMEDIATELY after the discharge, not leaving any time for the shooter to move to wash or wipe his hands. There is absolutely no activity before the collection of the samples. We’re also assuming that the shooter’s hands are clean. There is no debris or biological material (blood, sweat, saliva, etc.).

We’re also assuming that the area in which the firearm was discharged is contamination free. It’s clean and free of any GSR-related particles that may be present due to contamination from a previous discharge.

And finally, let’s assume that the room remained untouched after the discharge. There was no activity in the room that could cause particle movement or loss.
In this ideal scenario, we would expect for 100s to 1000s of GSR and GSR-related particles to be produced from the discharge of the firearm. It would be likely that a lot of those particles would be collected, and the conclusion of the testing would portray a large positive result.

Just a note, however: a large positive result doesn’t mean that you will hundreds to thousands of particles in your report, because in cases like that we will only confirm a representative number of particles to prove the positive result.

Slide 16
While having an ideal scenario would be excellent, we also recognize that it is not at all likely. So now let’s take a look at what we would consider some more realistic scenarios. A lot of these scenarios are ones that we get asked about a lot in court.

Let’s say that we have a situation in which a firearm was discharged in an area where there was definite airflow or weather considerations. Either inside or outside.

Now, let’s assume that the firearm was used is a poor producer of particles. Say it’s relatively closed off or sealed off and just doesn’t produce a lot of particulate.

Let’s also assume that the samples aren’t collected from the shooter until much later after the discharge – hours or even days, leaving plenty of time for the shooter to actively wash or wipe his hands or change his clothing.

We could also imagine that there was dirt, debris, or some type of biological material present on the shooter’s hands.

In these more realistic situations which we often get asked about in court, there is a variety of different outcomes which could be expected. It still is possible that hundreds to thousands of particles could be produced, and that a lot of GSR would be collected and analyzed. However, given these influential factors, that result is pretty unlikely.

What is more likely is that the analysis of these samples will show SOME GSR and GSR-related particles or even no particles at all. It’s important to note the reasons why samples may come back as inconclusive. There are many different factors that can contribute to particulate loss as mentioned.

Keep in mind that if at any point in time you have a question as to whether or not it would be probative to have a certain item of evidence analyzed, you can always give us a call and we can help you with any case scenario you may be curious about.

Many times in these more realistic scenarios, we will ask that you send any clothing that you might have for analysis as particles will tend to adhere more closely to the weave of fabrics than to skin.

Slide 17
So with all of these factors and all these different mitigating circumstances that could contribute to particulate loss, it seems that there could be a wide range of possible outcomes. This may lead you to ask the question, “Why, then, should I collect samples for GSR analysis?”

Well, there are several reasons.

  • FIRST, once GSR samples are collected, they can last indefinitely. Once the particulate is on the SEM stub, it’s not going to disintegrate or be lost over time. It is always better to collect the samples and then decide to not have them analyzed than to NOT collect them and NEED them later.
  • SECONDLY, collecting the samples creates a thorough case examination. In today’s world and in light of the “CSI Effect,” juries are coming to expect a complete and forensically sound case investigation. Not only does it create a full picture for a jury, but it also enhances your credibility as a witness on the stand.
  • LASTLY, and most importantly, GSR can be probative evidence providing strong investigative leads. Analysis by SEM is confirmatory. You can say definitely that there is a population of GSR present. It’s up to the jury to decide how it got there, but we can definitely confirm whether or not it IS there. GSR is a piece to the forensic puzzle. It works in conjunction with other evidence to create a complete case against an individual or individuals.

Slide 18
When we testify in court, there are some terms that you will most like be hearing which we are going to go over, and Stephanie mentioned these briefly. These terms originate from a group called “SWGGSR,” or the Scientific Working Group for Gunshot Residue. This is a group of gunshot residue experts all over the world who created a guide for the analysis of primer residue. This guide has become a standard in our field.

Within a population of GSR, you will most likely see a combination of three particle types, which SWGGSR refers to as “characteristic particles, particles consistent with gunshot residue, and particles commonly associated with gunshot residue.

Particles that are characteristic of GSR are particles that contain a combination of three important elements – lead, antimony, and barium. These particles are highly specific to the discharge of a firearm. When they are found on a sample without any other extraneous elements, we can say that they came from the discharge of a firearm.

Particles that are consistent with GSR are most often two-component particles, or particles that contain two of the three important elements. They contain either lead and barium, lead and antimony, and/or barium and antimony.

Finally, particles that are commonly associated with GSR are most often one-component particles, or particles that contain one of the three important elements of either lead, antimony or barium.

When talking about a “population of GSR” it is typical to see characteristic particles, as well as particles consistent with GSR and particles commonly associated with GSR.

Slide 19
Those three component, highly specific gunshot residue particles are confirmed on a sample, then we can say that the sample is positive for gunshot residue. When primer GSR is found, it means that one of these three scenarios occurred. The subject could have

  • Discharged a firearm OR
  • Been in proximity when a firearm was discharged OR
  • Came into contact with a surface or environment that contains GSR.

Each of these scenarios is equally likely or possible under MOST conditions. We say MOST conditions because there are some conditions in which one of the explanations is not as likely as another. For example, if you are collecting samples from a vehicle, the vehicle obviously cannot discharge a firearm. Therefore, if GSR is found in a vehicle, it means that a firearm could have been discharged in or near the vehicle OR someone or something that had GSR on them came into contact with the vehicle.

When no particles are found, or if ONLY one and/or two component particles are found, the results are deemed inconclusive. We don’t call this a “negative” result. The absence of characteristic particles does not necessarily mean that the subject did NOT discharge a firearm, or was NOT involved with a gun-related crime. It’s possible that there were particles on them at one point in time, but they could have been removed by factors that we went over previously. Because of this fact, we term results in which there are NO characteristic particles as “INCONCLUSIVE.”

Slide 20
Along with analytical results, there is a part of every GSR report that is called “Qualifiers.” RJ Lee Group includes this section, as do most other crime laboratories. This section QUALIFIES the results of the analysis and aids in the interpretation of their meaning.

RJ Lee Group includes three qualifying statements in GSR reports. We have already somewhat discussed these qualifiers, but for clarity’s sake they are as follows:

  • GSR can be deposited by circumstances such as discharging a firearm, being in the proximity of a discharging firearm, or coming into contact with a surface/object that has GSR on it. Again, when those highly specific characteristic particles are confirmed, each of these scenarios is a likely possibility as to WHY and HOW those particles got there.
  • Two-component and one-component particles are found in GSR but may also originate from other sources. Because one- and two-component particles can come from other sources aside from the discharge of a firearm, we cannot term them “characteristic”, but rather consistent or commonly associated with GSR.
  • The absence of GSR does not eliminate the possibility that the subject handled or discharged a firearm. Again, if samples are determined to be “inconclusive” or NOT have any characteristic GSR on them, it could mean that the subject did NOT discharge a firearm, but it could also mean that the particles were removed by some other means such as washing or wiping the hands, etc.

Slide 21
Along with the qualifying statements, there are a few other testimony considerations to be aware of that may come up during trial.

One of which is the fact that the FBI no longer analyzes GSR. We are often asked on the stand if we are aware of the fact, and we’re also asked if we’re aware no longer analyzes GSR samples because they consider it junk science. Well, we ARE aware of the fact that the FBI no longer analyzes GSR, but it is NOT because they believe it to be junk science. The FBI no longer analyzes GSR because they got less than ten cases per year involving GSR. The decision was then made to direct their resources to areas that were more closely related to their priority of combating terrorism.

The FBI still stands behind any and all reports that were issued concerning GSR in previous cases, and they simply forward on any current GSR case work to other laboratories that have the capability to test it.

The guide for Primer GSR analysis includes a memo from Marc LeBeau, the Chemistry Unit Chief of the FBI Laboratory stating just this. If you are interested in reviewing it, you can go to, and go to page 64.

Another consideration that we are often asked about during our testimony are other sources that create particles that are similar in nature to primer GSR. There does exist a very narrow category of sources that create particles that are similar to three-component GSR particles. Those sources include: a certain brand of nail gun and ammunition which is no longer being manufactured, a certain type of firework, the deployment of an airbag, or certain types of brake pad linings or brake pad dust. It’s important to note, however, that populations of particles from these sources may also include certain elemental tags that would indicate to an analyst that they are NOT looking at a population of particles from GSR. For example, particles coming from fireworks are likely to have magnesium or chromium in them; elements that are NOT typical in GSR. Or particles coming from brake dust also tend to have high amounts of iron with rigid or jagged morphologies. These are indicators to an analyst that the population is not GSR.

Along these same lines, it’s also important to take a subject’s occupations or hobbies into account. For example, a mechanic, who is more likely to have access to brake pads, or an avid hunter who is more likely to have gunshot residue or gunshot residue related particles on them.

One other consideration to mention is the fact that you, as police officers, can be a source of contamination. Studies have shown that it is possible to get GSR particles from the back of a police officer’s vehicle or from the handcuffs of a police officer who had cuffed someone previously. It’s not often a lot of transfer, but it IS possible. Because of this, we always recommend sampling at the scene. And if that is not possible, bag the hands of the subject before you place them in handcuffs or put them in the back of a police cruiser. And always, when collecting samples, be sure to where some form of personal protective equipment such as latex gloves.

Slide 22
As with any type of forensic testimony, there are some limitations to what we can say on the stand.
One of those limitations include the fact that we cannot age GSR. That means that if we find particles on a sample, we cannot say what incident put those particles there. The more recent the discharge, the more likely it is that the particles came from that incident, but it is still possible that they could have come from another, previous incident. When asked about that on the stand, we do have to say that it is not possible to link the GSR found to one particular incident over another.

It is also not possible to link the particulate found to a particular firearm. The majority of ammunition used is going to create the same type of particles – characteristic particles containing lead, antimony, and barium. Because these particles are produced with the vast majority of shootings, it’s not possible to link the particulate to one firearm over another.

And finally, again it’s important to note that as analysts, we cannot say WHO the shooter was. What we can do is confirm whether or not GSR particles are present. When they are present, it works as a piece to the case investigation. The jury decides how they got there, but we can confirm it.

Slide 23
This concludes our webinar “Analysis and Testimony Considerations.” Also be on the lookout for any other webinars coming at you on Distance Determination Analysis. I think that’s about all the time we have today, and I want to say thank you very much for joining us.

To read the Question and Answers at the conclusion of this webinar, please click here.