DNA on Guns

It happens every day all across America: You receive a radio call about an armed robbery suspect leaving the scene of a crime. En route to the call, you observe a man matching the description of the suspect walking along the street. He has his hands in his jacket pockets and is looking around nervously while he quickly walks down the street. You decide to stop him and of course, he bolts. A foot pursuit ensues, a perimeter is established and the suspect is found inside the perimeter, but not before you lose sight of him during the pursuit. When he’s captured, he’s unarmed. You search the pursuit route and locate a gun under a vehicle. Is it the suspect’s gun? It probably is. But, how do you prove it?

You can always rely on eyewitness testimony, but it’s often unreliable direct evidence, and you must have a witness that is both willing and able to testify to seeing the suspect in possession of the weapon.

Hands down, the best way to connect the gun to the suspect is by locating some sort of evidence on the weapon that will help identify the person or persons who have handled the weapon. In today’s forensic laboratories, this means fingerprints and DNA. You’ll need to recover the firearm and either process it for both latent fingerprints and DNA at the scene or send it to the lab to have the processing done. However, how do you render the firearm safe and still manage to preserve firearms, latent fingerprint and DNA evidence?

Preservation Is Key
Before the everyday use of latent fingerprint and DNA evidence, when a gun was recovered it was immediately rendered safe and booked for evidence, usually to match the gun to the bullet or for eyewitness identification. When latent fingerprint collection from a firearm became common, guns were handled only by the grip or non-smooth surfaces, preserving the smooth surfaces for latent fingerprint processing because latent fingerprints can be developed best on smooth surfaces. When you look at a gun, the best place to locate latent fingerprints is on the smooth surface of the barrel, the magazine or the ammunition.

Conversely, DNA-containing material is best found on uneven or rough surfaces where cells have rubbed off or collected in low spots. The best place to locate DNA evidence on a gun is in the ridges of the grip, hammer or trigger. So, with the advent of DNA analysis that has become increasingly more sensitive, guns should be handled and booked to preserve firearms, latent fingerprint and DNA evidence.

How do you decide whether you should process for prints or try to obtain a DNA profile? Essentially, it’s not an either/or situation. The good news is you can obtain both types of evidence from a gun. The bad news is that it requires the careful handling and processing of the gun to obtain the evidence and limit contamination.

DNA: The Genetic Fingerprint
DNA is the abbreviation for deoxyribonucleic acid, or the genetic material present in the cells of all living organisms. DNA is the fundamental building block for an individual’s entire genetic makeup. A person’s DNA is the same in every cell (with a nucleus), which means the DNA in a person’s blood is the same DNA in their skin cells, semen and saliva. The fact that no two individuals (with the exception of identical siblings) have exactly the same DNA makes it an ideal candidate for forensic use.

DNA is a type of physical evidence called biological evidence. Historically, the first type of biological evidence testing used in criminal cases was conventional serology. Typically, this involved testing the big three (blood, semen and saliva) in order to determine the blood type, blood grouping and/or the secretor status of the provider.

When DNA is analyzed for criminal-case purposes, the result is termed a “DNA profile.” The DNA profile can then be compared to known DNA profiles, commonly called standards, obtained from victims and suspects associated with the case, or it can be entered into the national database (CODIS the Combined DNA Index System) and searched against millions of convicted offender profiles nationwide.

In the mid-1980s, with the advent of DNA analysis techniques, the recovery and use of DNA for suspect identification became more prevalent. However, the tests required large samples of non-degraded biological evidence to obtain a DNA profile. Older DNA typing techniques required as much as 50 nanograms of DNA, or a bloodstain the size of a nickel. Testing techniques today require only about 1 nanogram of DNA, or a bloodstain the size of a pinhead, and the types of samples from which DNA can be obtained has increased exponentially.

DNA can now be recovered from almost anything that came from or has had contact with a human body, including urine, feces and vomit. It can be recovered from hair, weapons, masks, clothing, fingerprints, linens, cell phones, glasses, hats, shoes, ropes, gear shifts, steering wheels, car door handles, rear-view mirrors, utensils, water bottles, jewelry, combs, licked stamps and envelopes, etc. Just let your imagination take flight.

The sensitivity of today’s DNA typing is combined with statistical conclusions, which means it’s virtually impossible to find another individual with the same DNA profile. In fact, many forensic laboratories (including the FBI) consider DNA profiles rare enough to issue “source attribution” statements, which go so far as to state that the suspect with the matching DNA profile is the source of the DNA found at the crime scene (or, for the case in question, on the gun). DNA evidence has become an established part of the criminal justice system and the admissibility of DNA has become routine. DNA is now admissible in every state.

DNA analysis is similar to fingerprint analysis in how matches are determined. The evidence from the crime scene is compared to a known sample. Where the latent fingerprint, deposited by the fingertip pattern, is a complex mixture of natural secretions such as body oils and perspiration, the DNA is present in the skin cells that slough, or rub, off when a person handles an item. Thus, it’s possible for DNA to be obtained from latent fingerprints.

10 Do’s & Don’ts
The first rule for handling guns to preserve DNA evidence is to handle them as little as possible and wear fresh disposable gloves. The bottom line: The less handling of the gun, the less risk of contamination.

  • Do take your time, if the officer safety conditions allow. Of course, officer safety trumps evidence gathering techniques.
  • Do change your disposable gloves between recovering different pieces of evidence.
  • Do package the gun and its parts (ammo and magazine) separate from other forms of evidence such as clothing and cigarette butts.
  • Do recover DNA samples prior to fingerprint or firearms evidence.
  • Do use disposable fingerprint powder and latent brushes (available from forensic supply companies such as Sirchie), as the practice of using the same latent powder brush and reusing powder results in cross-contamination.


  • Don’t do anything but recover the evidence once you start.
  • Don’t talk over the evidence (spit contains DNA).
  • Don’t talk on your cell phone or radio (your cell phone and radio have your and other’s DNA on it). If you have to answer your radio before you have finished recovering the gun, change to a fresh pair of disposable gloves before continuing.
  • Don’t touch your face, rub your eyes or move your hair with your gloved hands (they all have DNA).
  • Don’t package DNA evidence in plastic. The moisture that is retained in the packaging promotes the growth of bacteria and mold that can degrade the DNA and render it unusable. Paper envelopes, bags and boxes are the preferred packaging because they “breathe” and allow moisture to escape. Render guns safe first and then secure them in a sealed gun box with plastic zip ties (otherwise, the gun could puncture through the box). Remove magazines and secure them in the gun box with zip ties.

Prevent Contamination
Contamination is a very bad word in the forensic DNA world. A contaminated sample makes it difficult and sometimes impossible to match a suspect’s DNA profile to the evidence, thus resulting in a failed prosecution due to reasonable doubt.

Contamination can result in mixtures of DNA from more than one person that can cloud the results and conclusions. Moreover, contaminated profiles can completely cover-up, or mask, the true DNA profile. This could mean that you’re spending time searching for a suspect that matches your evidence when in fact the DNA profile from the evidence is a contaminated profile. Newer DNA tests are based on sensitive technology, thus more attention must be paid to preventing contamination.

Contamination is defined as the undesirable transfer of material to physical evidence (DNA) from another source. Contamination in this sense really is the transferring of DNA from:

  • One piece of evidence to another;
  • The officer to the evidence; and/or
  • From another person to the evidence.

Contamination can occur if the officer touches the evidence with un-gloved or gloved hands. Unlike fingerprints that are not transferable from a gloved hand to an object, if an officer touches something with a gloved hand and then touches the evidence, the DNA from whatever was touched with the glove can be transferred to the evidence, thus contaminating it. In addition, if two pieces of evidence come into contact with one another, biological fluids or other DNA-bearing cells from one piece of evidence can transfer onto the other item of evidence leading to cross-contamination.

The next time you recover a weapon, remember that several types of physical evidence can be obtained from that weapon, including firearms, latent fingerprint and DNA evidence. It’s critical that you handle and process the weapon to reduce contamination and preserve the potential evidence.

In general, this means the item should be processed for DNA evidence before anything else is done. However, if you must process for latent prints first, use disposable brushes and powders to minimize the possibility of contamination that could render the item useless for court purposes.

DNA and latent print evidence must always be collected prior to firearms examination, as the extensive handling of the weapon required by firearms examiners will destroy any usable fingerprints and DNA evidence. With proper handling, the DNA evidence found on the gun that was hastily discarded by your armed robbery suspect can conclusively connect your suspect to the weapon, corroborate eyewitness testimony and ultimately can be very convincing evidence in a criminal prosecution.


Suzanna Ryan MS, is a forensic DNA analyst who has worked for both public and private DNA labs for 10 years. Most recently, she was the DNA Technical Leader for a private lab in San Diego. She also is an adjunct faculty member at National University in San Diego with the Master of Forensic Science program and an independent forensic serology and DNA consultant who provides DNA case-review services and expert testimony to both defense and prosecutorial agencies. Contact her at sryan@ryanforensicdna.comor visit www.ryanforensicdna.com.

Chief Betty P. Kelepecz (ret.), J.D., is a 25-year law enforcement veteran. Prior to retiring as a commander with the LAPD and later as the chief of the San Diego Harbor Police, she commanded the LAPD’s Scientific Investigation Division (crime lab). Before becoming a police officer, Kelepecz worked as a pharmaceutical microbiologist. Most recently, she was the lab director of a private DNA lab in San Diego. She’s a graduate of Southwestern Law School in Los Angeles, is licensed to practice law in California and is the president of Public Safety Consulting, Inc., a corporation that provides consulting services in the law enforcement and public safety environments. Contact her at bkelepecz@publicsafetyconsulting.net.

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