How to accelerate gunshot residue (GSR) analysis in forensic science using SEM

By Rose Helweg - May 28, 2019

jeroen-smuldersJeroen Smulders, physicist and product manager at Thermo Fisher Scientific, is part of the team that developed the Phenom Perception Gunshot Residue (GSR) Desktop Scanning Electron Microscope (SEM). This instrument is the only desktop SEM dedicated to gunshot residue analysis. Forensic scientists use the technique in order to find evidence that a suspect has discharged a firearm. In this interview, Smulders talks about the development history of GSR, explains details and handling of the Phenom Perception GSR Desktop SEM and gives examples for cases in which GSR is applied.

What was your first experience with GSR analysis?
In 2007 I started working at FEI (a microscope company, that is subsidiary of Thermo Fisher Scientific since 2016) as an application engineer. There, I have been responsible for the development of a desktop SEM. I followed the product to the spin-off company Phenom-World in 2009, where I worked for seven years as an application engineer. During this period I got in contact with GSR and we started developing an SEM dedicated to GSR analysis on the basis of the Phenom XL. We did our first GSR conference with the Phenom Perception GSR Desktop SEM in 2015 at the 22nd Annual ENFSI meeting for Firearms and Gunshot Residues.

Is the ENFSI meeting a special conference for GSR experts?
Exactly. ENFSI stands for European Network of Forensic Science Institutes. They host an annual meeting for forensic scientists. They even have a specific conference for firearms and gunshot residue, where ballistic and GSR trace experts come together. In order to make sure that we are in contact with the customers and the market, we attend these conferences.

You mentioned that the Phenom Perception GSR Desktop SEM is based on another product, the Phenom XL. What is the difference between the two?
The Phenom Perception GSR has an automated scanning routine that makes the biggest difference. And there are a few hardware options, which can be chosen for the GSR version, for example a motorized z-stage and a larger EDS-detector.

Are there any specific difficulties regarding the development of a GSR analysis SEM?

It is certainly a different game to develop an SEM that is suitable for GSR application compared to one that only makes good pictures and can do EDS-analysis for general samples. That mainly has to do with operational stability. For GSR analysis settings like contrast and brightness have to be maintained on a stable level for a long period since the procedure can take up to 24 hoursin extreme cases. So, the stability but also the accuracy of the Phenom Perception GSR are on a different level than of a regular SEM.

The accuracy, too?
Yes, the accuracy of the beam and stage positioning. For example: during scanning the routine detects a potential GSR particle. Afterwards it must go back to do an EDS analysis. Obviously, you do not want to analyze a spot just next to the particle. Or when you tell the stage to move 100 micrometer to one side you must be sure that is definitely 100 and not 110 micrometer. Otherwise you could miss a part of your sample and potentially GSR particles. In case that the stage moves less than 100 micrometer you might detect the same particle twice. Because of such reasons, a high accuracy of the instrument is very important.

But forensic scientists already use SEM to analyze GSR particles since the 1980s, right?
Indeed, GSR analysis with SEM started in the 1980s. With higher computer power and refined electronics it became more and more automated—and the results became more reliable.

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GSR particles are carried in the cloud of smoke after a gun discharge and deposited on shooters hand and surroundings

 

So in the beginning the operator used to sit in front of the computer screen and analyzed every single image by eye?
That’s a good question. I am not 100 per cent sure but I cannot imagine that the user analyzed every single image manually. For example: we used to work together with one of the pioneers in the field. And he wrote one of the first GSR software packages; it is not in use anymore today. However, it shows that already in the early days, the users tried to somehow automate the analysis process. And of course, over the years it has obviously improved a lot and sophisticated routine analysis methods have been developed.

In which year did your company start to develop the Phenom Perception GSR Desktop SEM?
We started in 2013. And in 2014 we announced that it is available as product. Since then is the only desktop SEM on the market that is specifically dedicated to GSR analysis.

Okay, let´s assume I work in a forensic lab and we have purchased a GSR microscope from your company. What are the first steps?
The first thing you will have to do is to customize the microscope, which means adjusting it to your individual requirements.

That means that the procedure of GSR analysis is different?
Not really. All the laboratories follow roughly the same procedure but the details in the settings are different. That is why you have to define how you want to run the microscope. There is a default run, but the chance that it matches exactly your way of working is quite low.

But there are standards for the GSR analysis?
Yes, of course. These standards for example define the size range of the particles and of the scan area. The guidelines are as specific as possible. However, they still leave some room for interpretations since quite some variables cannot be fully defined. Therefore, the way how the analysis is done, still varies from lab to lab—especially when you compare European with American or Asian forensic labs. Let´s say every forensic institute has its own way of working regarding the GSR analysis.

And your software provides this flexibility to do this customization?
Absolutely. There are tons of parameters, which can be adjusted to individual needs. You can for example optimize it for sensitivity or for speed and so on.

How long does it usually take to customize the system?
It can take up to several days or even weeks. But once you have worked out your standard operating procedure, then operating the SEM is super easy. You put in the sample, you focus manually and then you run the routine.

…and leave the microscope alone?
Right. So, on one hand you have a high flexibility but on the other hand it is very easy to use once you have set your standard way of working.

 

Discover the first dedicated gunshot residue solution 

The Phenom Perception GSR makes gunshot residue analysis on-demand, faster, easier, and more reliable than ever before. Download the specification sheet to learn more.

 

How many samples can you put in at the same time?
Up to 30 samples and there is space for some calibration samples.

For most of the customers that is more than enough. They usually analyze less than this amount at the same time. For instance, most of the laboratories do not mix samples from different suspects. Let us assume they have six different suspects. Then they do six separate runs—generally with three to five samples for each. By doing so they want to avoid cross-contamination or to simply prevent mixing up the samples.

What sizes do the samples usually have?
The most widely used sample holder is a sticky disc with 12 millimeter in diameter. That whole area can be analyzed.

How many particles do you typically find on a GSR sample?
Everything between 0 and 1,000 or even over 10,000's. It really depends on the circumstances, like on the gun that has been used, on the ammunition, or on the location: did it happen indoors or outdoors?

Do investigators also collect samples from a crime scene in order to detect if a firearm was used at all?
Usually there are much more obvious traces, for example a hole in the wall or cartridge cases on the floor. So, GSR is applied when there is evidence that a firearm was used. Not the other around.

The major source for samples is suspects then?
Yes, but it is also common to take samples from victims. It can for instance tell you if a victim has also used a firearm. Or cases that look like suicide: you can gather evidence whether or not the victim has used the firearm to kill himself. There will be much more GSR particles on the victim compared to a case in which someone else has fired the gun.

How many particles do you need for a positive outcome?
Obviously, when you find zero particles it is negative. But still it does not mean that there was no gunshot. And there is a debate whether already one GSR particle is a positive result. It really depends on who you ask. Some, for example, say we need at least three GSR particles.

And what does a positive GSR outcome mean?
It is widely agreed that GSR particles do only originate from firearms. However, they can be picked up through secondary processes. If you shake the hand of someone who has recently shot a gun, there might be GSR particles on your hand afterwards.

That means the presence of GSR alone is not evidence enough?
GSR is always presented as extra evidence. For example: if investigators find GSR-particles on your hand and your neighbor was killed last night, of course it does not mean that you are the one who killed your neighbor. It is just a part of a puzzle. And this part becomes stronger if investigators find many GSR particles on a sample and weaker if they find only a few.

 

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GSR analyses performed with a Thermo Scientific Phenom Perception GSR Desktop SEM

 

When there is no particle on the sample does the analysis happen faster?
Not really. It is not just scanning positive particles but instead you have to scan all particles on a sample in order to find out that they are negative. And typically, there are many environmental particles on a sample—usually between 1,000 and 5,000. Scanning all of them takes time.

Does that mean that the samples and particlesthat are suspicious by its morphologyare scanned again in more detail?
An energy dispersive spectroscopy (EDS)-analysis of the particle determines the chemical composition of the particle. By this it is possible to distinguish a GSR particle from any other particle. The chemical composition of GSR particles is very characteristic. At the end of the scanning process the user comes back and a report tells him how many GSR particles were detected. Now, the user has to verify and confirm that all these positive particles are indeed GSR particles. For this, a forensic analyst can make a high-magnification image for morphology reasons and do a manual EDS analysis for a high-quality EDS-spectrum.

How high is the error rate of the software?
In most of the cases the software is right. We do our best that the user has to reject positive particles as less as possible. I would say, our product is characterized by a low error rate.

So I guess the customer’s feedback is positive?
Well, what else can I say than yes? But I guess there are good reasons why our customers appreciate this product very much: typical forensic laboratories have large electron microscopes—and they do all kinds of forensic analysis with these instruments. SEM is not only required for GSR analysis. If someone runs GSR the SEM is occupied for several hours or even more. In this context for many forensic laboratories it makes sense to have an extra SEM, which is dedicated to GSR analysis only. And the Phenom Perception GSR is a small desktop SEM, which does not occupy much space and moreover, is fairly easy to use.

phenom-percepteption-GSR-desktop-sem-header-grey

Thermo Scientific Phenom Perception GSR Desktop SEM


Learn how to accelerate your gunshot analysis (GSR) analysis
GSR tests can make use of a scanning electron microscope (SEM) to scan the sample and identify suspect GSR particles. The Energy Dispersive Spectroscopy (EDS) technique is used to identify if gunshot residue elements like e.g. lead (Pb), Antimony (Sb), and barium (Ba) are present in the sample.

Because the system is automated, it enables you to speed up the forensic analysis process. The Phenom Perception GSR makes gun-shot residue analysis on-demand, faster, easier, and more reliable than ever before. Perfect for every busy GSR forensics lab that wants to save time and floor space. Learn more about our dedicated gunshot residue solution by downloading the specification sheet.

Download the GSR specification sheet

 


Topics: forensics, GSR

About the author

Rose Helweg is the Sr Digital Marketing Specialist for Thermo Scientific™ Phenom Desktop SEM. She is driven to unveil the hidden beauty of the nanoworld and by the performance and versatility of the Phenom Desktop SEM product range. She is dedicated to developing new relevant stories about high-tech innovation and the interesting world of electron microscopy.

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