Over the course of the last two decades, the use of DNA evidence has become a central component of the U.S. criminal justice system.
In 1987, Tommie Lee Andrews became the first person convicted on the basis of DNA testing in the U.S. when he was found guilty of rape and sentenced to more than twenty years in prison.
Today, law enforcement agencies regularly rely on large DNA databases to conduct criminal investigations, and defense attorneys frequently use DNA testing to show that innocent people have been wrongfully convicted.
As gun violence in the U.S. continues to rise, DNA evidence will undoubtedly be featured prominently in a slate of upcoming trials. With this in mind, it is worth exploring the use of DNA evidence as a practical legal tool—not simply as a plotline in “CSI.”
Unlike other forensic methods, such as fingerprinting and bite-mark analysis, DNA has been hailed for its accuracy.
“There is no doubt that, when compared to every other forensic science discipline—ballistics testimony, fingerprints, bite mark evidence, tool mark evidence, blood spatter—DNA testing is vastly more reliable,” said Jason Kreag, a UA law professor and former attorney for the Innocence Project in New York City. “It is the only forensic discipline that can consistently match crime scene evidence to an individual.”
As Kreag went on to explain, DNA testing is unique among the forensic disciplines in that it was originally developed for academic purposes. Researchers independently studied DNA for reasons outside the realm of criminal justice, and they validated DNA analysis methods in a purely scientific manner.
Techniques like ballistics analysis and fingerprint identification, in contrast, lack the same academic pedigree. Law enforcement officials developed most forensic methods for the sole purpose of solving crimes, and they did not necessarily adhere to the same high research standards as those who developed ways to analyze DNA.
Though founded on fundamental scientific principles, it would be remiss not to acknowledge potential problems with DNA testing, as it is used in the criminal justice system.
Indeed, one often-overlooked source of error in DNA testing is human fallibility. Mishandling samples, misinterpreting results and incorrectly reporting results can lead to erroneous convictions. For example, there have been documented instances of laboratories accidentally switching the reference samples of the victim and the defendant. It goes without saying that any conviction born from swapped DNA samples would be obscenely unjust.
“There are, of course, limitations to DNA evidence,” Kreag said. “Crime scene evidence, for example, is sometimes not like laboratory evidence. You might get a very partial DNA profile from a crime scene, which decreases its probative value as evidence.”
DNA evidence has two chief applications in the criminal justice system. Its first and most obvious application is for the identification of suspects. As seen on “CSI,” biological samples from crime scenes can be used to identify people present at the time of the offense. These samples can then, of course, be used to help prove that a suspect is guilty.
Second, and perhaps more importantly, defendants can use DNA evidence to prove their innocence, both during and after a trial. Though we often proclaim our legal system to be a flawless model of justice, the reality is that prosecutors charge innocent people and juries make mistakes. DNA testing provides a mechanism to help the truth shine through the murky waters of the criminal justice system.
“The exact same power that DNA gives law enforcement … to solve crimes has provided a way for people who are accused of crimes to prove their innocence,” Kreag explained. “Even though probably less than 10 percent of criminal cases hinge on DNA evidence, the DNA innocence cases should give us all pause. We should realize that there are probably more out there like them.”
As the recent series of gun violence cases unfold in the criminal justice system, forensic evidence will surely come into play. Ultimately, a few defendants might find their futures resting on the information contained in the deceivingly simple double helix known as DNA.
Follow Elizabeth Hannah on Twitter
