We’ve all seen episodes of crime shows that feature investigators finding a hair at a murder scene and solving the crime with a DNA match. However, real life is far from a television script, and the truth is that DNA evidence does not always positively identify a suspect. Members of juries who are not familiar with the criminal justice process may believe that they know how crimes are solved from watching TV and movies. Therefore, juries may often feel completely convinced—beyond a reasonable doubt—about a defendant’s guilt when the prosecution presents DNA evidence. It is a defense attorney’s job to dispel the myth that DNA evidence is infallible.
What Can Make DNA Evidence Unreliable?
A good criminal defense attorney can call DNA evidence into question for several different reasons. First, people can leave their DNA anywhere they have been, and it does not necessarily mean they committed a crime in that location. For example, imagine John visited Paul at Paul’s home at 7 p.m., then left at 8:30 p.m. Mike then entered the home and committed a murder at 8:45 p.m. Police investigators find DNA in the home that matches John and arrest him. If the jury based its verdict on the DNA evidence, John would receive a wrongful conviction. Also, the DNA does not have to be left near the time of the crime. Under the right conditions, DNA can survive intact on a surface for weeks, months, or even longer.
In addition, research has indicated that DNA can transfer from one person to another during routine daily behavior. If John shook Mike’s hand and then Mike killed someone and touched an object at the crime scene, investigators might find both John and Mike’s DNA there. If there is a match to John but no match discovered to Mike, John could again receive a wrongful conviction. Or the DNA of both Mike and John could be discovered and John could be wrongfully accused and convicted of participating in the murder with Mike.
Transfer of DNA is only one reason that prosecutors or juries should not rely solely on this evidence. In addition, forensic labs that analyze DNA can make errors in the handling or testing of a DNA sample. It is imperative that labs store and handle all DNA samples properly to prevent contamination. If a DNA sample is contaminated in any way, it can cast doubt upon the reliability of the lab’s findings.
Furthermore, mislabeled samples or those mixed up with other evidence may lead to completely unreliable results.
Another important matter with any evidence, but especially DNA, is called the “chain of custody.” Every time a DNA sample changes hands—from investigator to lab to storage—it must be clearly documented. Anytime a sample is not fully accounted for, there an opportunity for contamination or tampering. An experienced defense lawyer knows how to closely examine the chain of custody records and identify any gaps that may cast doubt on the DNA evidence.
Finally, DNA testing is not an absolute science. Testing DNA samples and evaluating results involves human judgment and decision-making at many levels. In fact, two analysts running the same tests can come to different results. Even if a lab technician reports a DNA match to a defendant, the jury must understand that human error could cause the lab results to be unreliable.
Casting Doubt on DNA Evidence at Trial
In cases involving DNA evidence, an experienced criminal defense attorney should know how to effectively show the jury that such evidence can be unreliable. The process can begin during jury selection by asking which jurors watch crime shows, determining who would absolutely believe DNA evidence, and striking them from the jury. During trial, an experienced criminal defense attorney can cast doubt on the DNA results through cross-examination of the lab technicians who testify to the match, calling into question the reliability of their results. Your criminal defense attorney can also present experts as defense witnesses who can inform the jury about the fallibility of DNA evidence in general and any problems with the specific DNA testing done in the case.
Discuss Your Case With Our Connecticut Criminal Defense Attorneys Today
At Koffsky & Felsen, LLC, our experienced criminal defense lawyers know how to handle the most complex cases, including those involving DNA evidence. If you were arrested or charged with a crime, please call our office at (203) 327-1500 or contact us online today to discuss how we can assist you.