Is DNA evidence always foolproof?

Is DNA evidence always foolproof?

DNA made its first appearance in the mid-1980s, but it wasn’t until 1987 that it became an integral part of the U.S. criminal justice system. On February 5 of that year, an Orange County, Florida jury convicted serial rapist Tommy Lee Andrews after tests matched his DNA to a semen sample taken from one of his victims. Since then, DNA evidence has come to be regarded as irrefutable: according to a 2005 Gallup poll, 85% of people saw it as “very” or “completely” reliable. That’s a lot of faith in a process that, for all its advantages, is as vulnerable to errors and mishandling as any other.

Common examples of DNA evidence collected at crime scenes include:

  • Semen
  • Blood
  • Skin particles
  • Hair follicles

The larger the sample, the easier it is to test for accurate results, but errors still occur. Below are three common mistakes related to DNA evidence.

Timing issues

This problem often occurs when the suspect had an intimate relationship with the victim. Pinpointing exactly when biological material such as saliva or semen was left is difficult to do, so it’s entirely possible that (for example) a semen sample collected from an alleged rape victim was the result of consensual sex.

When investigators search for DNA evidence at a crime scene, they can theoretically collect samples that were in place for months before the crime occurred. When this happens, an innocent person could end up being questioned and even charged.


The police don’t always follow the correct procedure for handling and storing DNA evidence. When this happens, samples can become contaminated and useless in a criminal court proceeding. Humidity, heat, exposure to sunlight, and even the passage of time can all impact the quality of DNA evidence and yield faulty test results.

“Touch DNA”

Touch DNA refers to the way that skin cells attach to an object after someone touches it. If you shake hands with another person and they proceed to touch a doorknob, they can deposit your DNA onto the knob instead of theirs. If that door is later believed to mark the exit route of a criminal, your DNA can show up and turn you into a suspect.

DNA evidence is not always right, but faith in it is so strong that it can send innocent people to jail. If you are accused of a crime, and the prosecution claims that DNA evidence has conclusively proven your guilt, then don’t be fooled. Carelessly collected and stored evidence, sample contamination, and even mistakes in the lab can all result in false positives.

Instead of cutting a deal for a crime you did not commit, contact an experienced New York defense attorney. Julie Rendelman is a criminal defense lawyer with a conveniently-located office in Midtown Manhattan. She has over 20 years of legal experience including many years as a prosecutor. She works hard to protect her client’s rights. She can examine the circumstances under which the DNA samples were collected, handled, and stored, and take all supportable measures to help you clear your name. Call 212-951-1232 for a free consultation or to schedule an appointment.