How DNA Testing Made Its Way Into The Legal System

October 7, 2021

By a Biometrica staffer

Well over 700 years ago, Song Ci, a Chinese judge, is said to have personally examined the crime scenes of physical assaults or difficult murders. His book, The Washing Away of Wrongs, was written around the year 1247 and became what is recognized today as the oldest existing text on forensic science. His manual, meant to help bureaucrats navigate the complex process of judicial inquiry, is said to predate the earliest European texts by hundreds of years. The book explains how to determine which wound was the cause of death, distinguish between ante-mortem and post-mortem injuries, and differentiate between accidental deaths and homicides.

What’s more fascinating is that China had already been conducting forensic assessments for violent or suspicious deaths for centuries before Song Ci’s book was published in the mid-13th century. Bureaucrats — and not full-time detectives or forensic scientists, as is the norm today — were responsible for leading inquests as a small part of their duties. Regardless, it establishes the fact that forensic science was used in criminal investigations and the justice system even in medieval times.

Still, the use of one forensic tool has been a subject of much debate within the US: DNA testing. In this piece, we tell you in brief how that tool made its way into the country’s legal and criminal justice system.

But what exactly is DNA analysis or testing? In simple words, DNA testing or profiling can be used to identify individuals on the basis of their unique genetic makeup. Multiple people may share physical similarities, from eye and hair color to facial features, but they won’t have the same DNA. This is what makes it a useful tool when it comes to solving crimes.

Those who are not wholly in support of using DNA have claimed that it is an unreliable tool that can lead to the wrongful conviction of innocent people. Law enforcement agencies and prosecutors, on the other hand, are eager to use the benefits of DNA evidence to help combat crime. Ultimately, since it was first made admissible as evidence in courts in the US in the 1980s, it’s now become a valuable tool, particularly since biological material (skin, hair, blood, and other bodily fluids) has emerged as the most reliable physical evidence at crime scenes.

This whole journey started in the second half of the 1980s. Throughout the year 1986, police in Orlando, Florida suspected that one man was involved in over 20 cases of prowling, breaking and entering, and attempted sexual assault, per a publication by Princeton University, titled “DNA as Evidence.” In each case, the modus operandi was similar: the man would stalk his victim for weeks, prowling around her house and peeping through windows. When attacked, the victim had little or no opportunity to make a visual identification.

Until Tommie Lee Andrews was arrested, the only thing police had to go on were composite drawings and several calls about a prowler. After his arrest, one rape victim managed to pick Andrews out of a photo lineup despite only having seen him for all of six seconds. It was only after the prosecutor in the case, Jeffrey Ashton, read an advertisement in a legal publication about DNA testing that he discovered it could be used and, thus, he employed the services of Lifecodes Corp. for that purpose. That’s when Hal Uhrig, who was appointed Andrews’ defense attorney, realized that he was involved in the first known DNA criminal case in the US, the DNA as Evidence publication says.

DNA test results were introduced at Andrews’ very first trial by prosecutors, only to have the introduction of any testimony regarding the statistical probabilities resulting from the test successfully challenged by the defense. The trial ended in a hung jury. But DNA evidence was, once again, introduced at the retrial. This time, the prosecution was prepared to argue that statistical probabilities relating to the test should be introduced.

The court used a relevancy standard similar to that in the Federal Rules of Evidence, which governs the introduction of evidence at civil and criminal trials in the U.S. federal trial courts, and admitted the statistical data. Andrews was subsequently convicted.

Since then, DNA testing and evidence has been used in several other cases. The very year after Andrews’ trial, for instance, it was used to sentence a Virginia killer known as the “South Side Strangler” after DNA linked him to several rapes and murders around Richmond, says a Time Magazine article. It is also responsible for snaring Gary Ridgway, the infamous “Green River Killer” of Washington State, responsible for a string of murders around Seattle in the 1980s and ’90s. After being implicated by genetic testing, Ridgway pleaded guilty and was sentenced to 48 consecutive life sentences. 

There have been many other cases where DNA evidence has played a key role through the years. In July 2001, a Milwaukee, Wisconsin appeals court judge upheld the validity of a criminal warrant for the arrest of “John Doe 12,” issued for a 1994 rape case just days before the statute of limitations was to expire. This was the first known case in which prosecutors sought arrest warrants based solely on a DNA description. When a DNA evaluation matched the DNA of “John Doe 12” with that of Bobby Richard Dabney Jr., the state replaced the placeholder name with Dabney’s, a post on law.jrank.org says.

Today, the use of DNA testing and evidence in the legal system is widespread. There are laws governing when DNA can be taken, why DNA can be taken, how DNA information can be kept, and what the qualifications are for labs that handle it, which vary from state to state. Your rights as a victim of a crime or as a person who has been accused of a crime vary a great deal depending on what state you are in. In many states, law enforcement is authorized to collect DNA upon arrest, but which crimes qualify are very different from state to state. In some states, a probable cause hearing is required first, but in others it is not. 

How exactly DNA is collected, what qualifies as types of samples, and the basis of analyzing it are also interesting. But that’s a story for another day.