January 22, 1988. This was the day that Colin Pitchfork of Leicestershire, England, stood before a judge and was sentenced to life imprisonment for the rape and murder of two 15-year old girls. Pitchfork was identified as the killer and confessed to both crimes when confronted with DNA evidence.

Catching Colin Pitchfork

The concept of DNA was studied for many years, and in 1984 Alec Jeffreys, a professor at the University of Leicester, was able to prove that the DNA profile of each person was unique.

In 1983, a teenage girl was found raped and murdered in Narborough, Leicestershire. Semen sample was found near the body. In 1986, another teenage girl was found raped and murdered in neighboring Enderby village, and the semen samples found near the body showed the same blood type.

Since the case occurred near the University of Leicester, the police authorities in the area knew of Sir Alec Jeffrey’s techniques. Using DNA testing they were able to prove that both girls were murdered by the same man and that one man who confessed to the crime was not the actual killer.

In 1987, the police took blood and saliva samples from about 4,000 men aged between 17 and 34 years old who lived in the nearby areas. They started with men who didn’t have an alibi, and later expanded the screening to men who had an alibi. No match was found.

Later a man was overheard saying that he submitted DNA material for a friend. That friend’s name was Colin Pitchfork, and he was arrested on September 19, 1987.

The police matched his actual DNA profile to the DNA profile in the semen found near the bodies of the victims. Confronted with the evidence, Pitchfork finally admitted to his crimes. He was already a convicted flasher, admitting that he gets excited when the victims ran away from him.

The arrest and conviction of Pitchfork led to the use of DNA profiling in many parts of the world particularly in the US. Here is an episode of Real Crime featuring his story:

DNA And The Future

By now everyone has a basic understanding of DNA and how each one has a unique DNA just like each person has a unique fingerprint. It stands for deoxyribonucleic acid, and it refers to the genetic material in every cell in our body. Each person has a unique DNA profile, and the DNA can be extracted from the hair roots, skin, semen, blood, saliva, sweat, and mucus found in a crime scene. DNA can survive for centuries, so crimes committed many years ago can still be investigated.

In the past, the main problem with DNA is in cases involving identical twins, who come from the same egg. Only a small fraction of the DNA code needs to be analyzed to show the difference between 2 average people. But a standard DNA test would show the same profile for identical twins.

Fortunately nowadays it’s already possible to analyze the entire 3-billion-letter sequence to find the differences in the DNA profiles of identical twins.