Popular crime shows would have you believe that the analysis of forensic evidence is the key to finding the perpetrator of a crime. But is forensic evidence reliable? DNA evidence, blood spatter patterns, bite marks, finger prints and other common types of forensic evidence have been subjected to scrutiny and some just don’t hold up. For example, I previously wroteabout an innocent man who spent 33 years in prison based on bite mark analysis – a forensic evidence technique that has been discredited in the scientific community but continues to be used by prosecutors.
Similarly, other forensic analysis methods have been questioned, or even debunked, by science but continue to be an important part of the prosecution’s arsenal. In the popular imagination, these techniques provide a slam-dunk conviction. But most members of the public, from whom a jury of peers is selected, would be surprised to learn—and perhaps even reject—the proposition that quite often forensic evidence is nothing but junk science. Overcoming this bias takes the persuasive skills of criminal defense attorney who is up on the science and can communicate a reasonable doubt about the forensic evidence.
Here’s one that may surprise the average reader: Even positive DNA evidence may not be evidence at all. The common assumption is that if a suspect’s DNA is found on the victim or at a crime scene, the suspect is positively implicated in the crime. But that is not always true. Often the DNA evidence is in trace amounts but is thought to be conclusive evidence of the suspect’s presence at the scene. DNA analysis has become so sophisticated that forensic technologists can pick up even the smallest amounts of DNA. The problem is that humans shed DNA all the time and everywhere. When you touch anything, you will leave your DNA. Another person touching the same object can then pick up your DNA. This is referred to as the “touch-transfer” property of DNA. So, imagine that you took a public bus. Another passenger on that bus picked up your DNA and shortly thereafter committed a crime. Your DNA may very well show up in forensic analysis, implicating you in the crime.