Sir Alec JeffreysSir Alec Jefferys

DNA: The First Exoneration and Conviction

By: Joseph Giacalone

In my first Forensic Rock Star post, I highlighted the important contributions of Edmond Locard. Today’s post will continue with the Forensic Rock Stars that have shaped the world of criminal investigations. Dr. Sir Alec Jeffreys is the reason why investigators all over the world search for evidence that contains DNA, the genetic blueprint of all human life. His discovery led to the transformation of how law enforcement manages crime scenes, how evidence is identified, secured and packaged properly.

Many people erroneously believe that the first time DNA was used to solve a crime was in the United States. It wasn’t. In a small town in England known as Enderby, two teenage girls, Lynda Mann and Dawn Ashworth, were raped and murdered a few years apart in the same general vicinity. The police were limited on what they could derive from genetic material left at crime scenes. Analysis of the semen found at the scene provided the perpetrator’s blood type as “A.”

Not only did this case get the first conviction based on DNA, but it also exonerated the first person, Richard Buckland, who initially confessed to murdering Dawn Ashworth. The police sought the help of Dr. Alec Jeffreys and his discovery of DNA profiling. Dr. Jeffreys’s findings also included that no two person have the same DNA profile, except identical twins. The police suspected that Buckland was responsible for both murders, however, Dr. Jefrreys confirmed that Buckland was not the killer of either woman – the DNA profile said so. Armed with the profile the police asked all men in the area to submit a sample for testing against the profile. Thousands of blood samples were taken and tested but no match. The police were stumped, until they received a phone call about a man in a local bar claiming to have been paid to take the test for someone. After questioning the man, Colin Pitchfork was arrested and subsequently convicted. This time the confession was backed by the DNA profile. Recently, Colin Pitchfork has had his appeal denied.

Types of DNA

There are two types of DNA that are found in the body: Nuclear and Mitochondrial. However, not every cell in the body contains nuclear DNA. Nuclear DNA is the preferred finding by investigators because it contains genetic material from both parents. Mitochondrial DNA (mtDNA) does not have a nucleus and therefore does not contain genetic material from both parents. When investigators only have mtDNA, they must find a match that is derived from the maternal side. The way I always remembered it was M (mtDNA) is derived from Mom.

What is CODIS and how does it work? 

CODIS is the acronym for the Combined DNA Index System. It is a nationwide system of storing and securing DNA samples. Inside of CODIS, two additional databases can be found: The Forensic Database and the Convicted Offender Database. It is easier to remember them as such: The Convicted Offender Database is the “Known” sample database and the Forensic Database contains the samples from crime scenes where the perpetrators are “Unknown.” Because it is a nationwide system, each state has developed its own DNA Index System to alleviate conducting nationwide searches for what is more likely, local suspects.

How should DNA Evidence be Packaged?

All evidence that may have body fluids such as blood, saliva, semen, etc., must be packaged in paper and never in plastic. Unfortunately, law enforcement learned the hard way from all of those years that evidence was put in plastic security envelopes. Plastic over time degrades the sample due to moister buildup, rendering the sample useless in most cases.