If you watch television crime dramas, or crime scene investigation shows, you may have seen an episode or two where DNA evidence helped to convict or exonerate a suspect. But do you know how DNA evidence is used in criminal prosecutions? We are going to look at how DNA evidence is used to help solve crimes and find out what DNA profiling is. The topic of DNA is a complex one, so we are going to simplify these concepts and discuss the bare basics and how they apply to using DNA evidence to solve crimes.
What is DNA?
DNA is an acronym for deoxyribonucleic acid, which is the molecular blueprint for the human body. All human beings have DNA and collectively, the human genome is approximately 99.9% identical. Therefore, regardless of where you go on the planet, human beings all have two eyes, two ears, hands, feet, etc. The 0.1% difference accounts for all the individual traits that make you unique. No one else on the planet has or ever will have DNA identical to yours unless you have an identical twin.
DNA profiling or fingerprinting is the process of isolating that fragment of your DNA sequence that is uniquely yours.
Using DNA to solve crimes began in 1985 in England when Alec Jeffreys first used DNA evidence collected at a crime scene in an investigation. Where law enforcement used to rely on fingerprints and eyewitness testimony, DNA is now standard in crime scene investigation. When a person is in a location, they tend to leave behind trace amounts or greater amounts of hair, saliva, blood, semen, sweat, skin cells or mucus. Because of the rapid advances in DNA processing, forensic scientists can recover DNA fragments in increasingly smaller bits of evidence from a crime scene.
Again, referring to those crime scene dramas, you might remember that the police often put plastic coverings over their shoes, wear gloves and use tweezers or some implement to pick up and bag an object that they suspect might contain DNA so that they do not contaminate the object with traces of their own DNA.
Sources of DNA evidence at a crime scene
There are endless numbers of places where DNA can be collected from a crime scene to place a suspect at the scene, or rule out their presence there:
- The weapon, which could contain blood, skin cells, sweat or other bodily materials
- A hat, which could contain hair, sweat or skin cells from the scalp
- The victim or the clothing the victim was wearing
- Bits of fingernail
- Bed linens
- Cigarette butts, bottles, drinking glasses
Detectives and crime scene investigators try to handle the evidence carefully, photograph the item, bag it and label the item for further forensic testing.
What is CODIS?
The DNA collected at a crime scene would have to be matched to make a comparison. The victim’s DNA will be taken for comparison. When a suspect is arrested, some jurisdictions might collect a DNA sample when they take their fingerprints and process or “book” them. The FBI maintains a DNA database. CODIS is an acronym for the combined DNA index system and it contains DNA profiles that local, state and federal law enforcement collect.
When a crime is committed, law enforcement can compare the DNA recovered from a crime scene against the CODIS database to try to find a match.
Why DNA results cannot always be trusted
DNA is everywhere. Imagine a crime that took place after a party where 30 or more people occupied the same space and touched nearly everything. Isolating the DNA samples of the perpetrator and the victim, eliminating the countless other DNA fragments that will also be found on an item can also be complicated. Since this process is undertaken by human forensic lab technicians, there is room for error. While DNA fingerprinting has revolutionized crime scene forensics, it is not as simple as the TV dramas portray it to be, and it is not always 100% accurate.
DNA evidence can be used to place a suspect at the scene, it can be used to exonerate a suspect, but it is not always 100% accurate. DNA results can be challenged. Working with an experienced Sevierville criminal defense attorney will ensure that your rights are protected.
A skilled criminal defense attorney from Delius & McKenzie, PLLC can defend the presumption of innocence on your behalf. To set up a free consultation with us about your case, call 865.280.3686, or complete our contact form. We are here to serve you in and around Sevierville, Gatlinburg, Seymour, and Pigeon Forge.