By Michael Yoder, Retired FBI Criminal Profiler
By now, everybody has heard of DNA and what an amazing forensic tool it is for solving homicide investigations. If there is a DNA match at a crime scene, the DNA belongs to only one person on the planet (unless there is an identical twin). Scientifically, the FBI estimates a DNA match to be around 1 in 113 billion – WAY more than there are people on Earth. Since its discovery and ongoing refinement of its analysis, DNA remains the gold standard of forensic tools. Every detective yearns to solve homicides with a DNA match to ensure a fair verdict. Non-matching DNA can clear a suspect, saving law enforcement resources.
DNA (Deoxyribonucleic acid) is a molecule that contains genetic information for an organism’s development and function, consisting of two chains that coil around each other to form a double helix. DNA is present in blood, saliva, semen, hair follicles, tissue, perspiration, urine, feces, bone, teeth and skin cells. It is microscopic and invisible to the naked eye.
Though DNA is valuable in solving homicides and uncovering the truth, there are challenges in using DNA analysis effectively. Three primary obstacles include obtaining DNA samples, matching DNA found at a crime scene to a DNA database, and finally, putting DNA evidence in perspective of the crime scene.
The first obstacle is obtaining DNA evidence. An investigator must identify likely locations for DNA, then blindly extract the microscopic DNA, collect it in a sterile container and send it to the crime lab for analysis. Results often take several months, and DNA analysis is expensive. So, the investigator must make smart choices on what to analyze and what not to analyze. This knowledge comes exclusively from experience and a thorough analysis of the crime scene.
The second obstacle is in matching the DNA sample collected at the crime scene to a DNA database that contains biographical information of the owner. In 1994, Congress passed the DNA Identification Act which authorized the FBI to create a national DNA database of convicted offenders. The FBI formed CODIS (Combined DNA Index System) that provides access to local and state crime labs. Crime labs can compare DNA profiles electronically from any participating crime lab and identify suspects by matching DNA from crime scenes to convicted offenders.
As of September 2020, CODIS contained more than 14 million offender profiles. While this is a large number, if you compare it to the population of the U.S. (roughly 300 million), the chance of a match is less than 5 percent. Additionally, when accounting for births and deaths since CODIS’s inception, the percentage is further reduced. By comparison, civilian genealogical companies like Ancentry.com have over 22 million DNA profiles, 23andme.com over 12 million DNA profiles and MyHeritage.com over 6 million DNA profiles. With only a few exceptions, these civilian companies do not cooperate with law enforcement’s request to compare their DNA profiles taken at crime scenes to their database. The conclusion is that the chance of a DNA match of a profile collected at a crime scene to a known DNA profile is exceedingly small.
The third obstacle to the use of DNA in a homicide investigation is putting the matched sample in perspective of the crime. DNA is non-biased and purely scientific; however, DNA samples are not time stamped. A DNA sample cannot indicate if it was deposited an hour ago or a year ago. It only states the DNA sample was left at that particular place. Unfortunately, DNA matching in a violent crime between two people who know each other well may not be an effective tool since their encounter may have been from a non-criminal activity in days, months or years past. It is up to the investigator to determine that a suspect (who is potentially lying) was not supposed to be at that location.
If you’re passionate about true crime and want to learn how to become a sleuth, join the Destin True Crime Club on Facebook. We meet monthly to investigate a real cold case and share research ideas. It’s a serious—but fun—group of dedicated individuals. Questions or speaking requests? Email myoder0361@gmail.com.
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