College of Criminal Justice News

Tuesday, December 4, 2012

Alumnus Links Weapons to Crimes

Firearms Examiner Kevin Callahan prepares to fire a large caliber revolver in a water tank during training.
Firearms Examiner Kevin Callahan prepares to fire a large caliber revolver in a water tank during training.

In one of his most memorable cases, Firearms Examiner Kevin Callahan (MSFS ’08) used a fired shotshell found in a suspect’s possession – as well as a test fire from a non-functioning shotgun – to link the suspect to a crime scene where two women were sexually assaulted and shot. His analysis assisted in the filing of a murder charge.

Callahan cuts a gun to make it operable.
Callahan cuts a gun to make it operable.
Callahan was recently recognized by the Texas Department of Public Safety Commission, a board of five appointed officials that oversee policy at DPS, for “thinking outside the box” in devising a method to retrieve a test shell from the inoperable pump action shotgun, which had a crushed magazine tube and forearm. Callahan cut one of two struts connecting the forearm to the action of the gun allowing him to cycle the shotgun with a pair of pliers and fire a sample shotshell that matched those found at the crime scene.

“I presented the case to the DPS Commission of a double sexual assault, homicide and attempted homicide,” said Callahan. “The shotgun that was recovered was initially inoperable, but I was able to render it functional for my analysis, albeit unconventionally. It was one of those cases that reminds you of why you got into the field in the first place.”

Callahan presented his case to the Texas Department of Public Safety Commission.
Callahan presented his case to the Texas Department of Public Safety Commission.
Callahan found his niche in forensic science at the Department of Public Safety Crime Lab in Lubbock, where he handles about 8 to 10 firearm and tool mark cases a month. He will soon move to the Garland DPS office, where he may be cross-trained in other aspects of the state crime lab, such as controlled substance identification or toxicology.

Callahan credits Sam Houston State University with giving him a leg-up in his career. In fact, three graduates of the program were hired as firearm examiners for DPS labs. Ryan Mudd (MSFS ’07) is working in the Austin Crime Lab, and Jeff Kelly (MSFS ’09) is still in training and will be assigned to El Paso.

“For every class I took in the program, there is somebody in the Crime Lab that applies it directly in their work,” said Callahan. “Having been in this discipline for a while, I can see the difference in various forensic programs. I’ve always been very proud of the Sam Houston program. It is top notch.”


Cartridge case match from a 9mm Luger fired from a Baretta 92D pistol.
As a member of the crime lab team, Callahan uses unique firing marks on bullets, cartridge cases and shotshells to tie them to firearms and other pieces of fired ammunition in criminal cases. In addition, he performs tests to determine the distance at which a shot was fired.

Callahan usually begins an investigation by ensuring the gun is functional and shooting test fires into a bullet recovery water tank. That firearm uniquely marks bullets with a pattern of lands and grooves, which are compared to known evidence using a comparison microscope, which is a side-by-side microscope connected with an optical bridge. He also can compare unique marks made by tools, such as those used in burglaries or in copper theft cases, using similar techniques.

The comparison microscope allows Callahan to compare images side by side.
The comparison microscope allows Callahan to compare images side by side.
To determine the distance used in shootings, Callahan has a stereo- microscope to examine gunshot residue patterns left on clothing. In addition, infrared cameras and chemical testing are helpful to identify the muzzle to target distance.

Finally, Callahan uses the National Integrated Ballistic Information Network, a nationwide database that compares cartridge cases found at crime scenes and test fired from submitted firearms, to help with cold cases. The database stores images of the unique markings on fired ammunition which can then be searched to see if a gun can be linked to another crime or arrest.

Bullet match for 380 auto caliber from Walthers PPKS-1 pistol.Bullet match for 380 auto caliber from Walthers PPKS-1 pistol.Callahan’s passion for forensic science began as a Boy Scout earning his merit badge in fingerprinting. He was fascinated after the Scout Master lifted his prints from a Coke can and uncovered the loops and whorls.

“At that age, it was amazing to me that a person could leave evidence behind without even knowing it,” said Callahan.

As an undergraduate, Callahan found he preferred Chemistry to Biology, and he landed an internship with the Southwest Institute of Forensic Science in Dallas. After working on autopsies in the morning, he spent the afternoon observing various forensic disciplines. The most enthusiastic worker at the institute was a firearms examiner, and Callahan quickly followed suit.

“You could just tell that he loved his job and what he did,” said Callahan.

As a graduate student at Sam Houston State University, Callahan took a second internship specializing in the firearms discipline with Harris County Sheriff’s Office, which solidified his career choice. Upon graduation Callahan was hired by DPS and after fourteen months of training followed by four working cases under supervision, he was assigned to Lubbock.

“The program at Sam Houston was pretty tough,” said Callahan. “The training I received at DPS was much more specific, but it wasn’t any more or less tough than what I received at Sam. It included tests, proficiencies and competencies.”

Testing an AK-47 rifle.
Testing an AK-47 rifle.
Callahan said the program at SHSU is “science based” and provides a comprehensive introduction to the disciplines in forensic science. For Callahan, it offered insight on how the crime lab can work together to process evidence more completely and efficiently. For example, Callahan can recognize blood or trace evidence on weapons, which can be processed by those sections. The education he received from Sam also allows for better preparation for cross training so that he can work in other areas in the lab if his caseload is low.

“At Sam, I got a well-rounded knowledge of the field,” said Callahan. “I can see how all the forensic sections can work together to process evidence. Because of this, I was a much better candidate for employment and I think it will continue to serve me well throughout my career.”


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