History of DNA testing in criminal cases

Written by michelle l. guffey
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DNA testing has only been around for about 24 years, but it can mean the difference between life and death for many people charged with---or convicted of---crimes.

The Facts

With the exception of identical twins, all humans have a unique DNA that is present in their skin, hair, blood and other bodily fluids. Because of this genetic fingerprint, forensic testing has become an invaluable source of physical evidence for law enforcement in obtaining convictions and in exonerating the wrongly accused.


In 1985, Professor Alec Jeffreys of the University of Leicester discovered that each person carried a genetic fingerprint in his or her DNA. This discovery was first put to the test in an immigration case; a year later, DNA profiling was used in a criminal case---a double homicide in England---and helped prove the innocence of a man who gave police a false confession. The DNA obtained from crime scenes in 1983 and 1986 proved that the same man raped and killed the two young girls. With the killer's DNA on file and new crime fighting technology at their disposal, police collected blood samples from more than 5,000 men in the community. The killer was eventually caught. In the United States, in 1987, a rapist in Florida was the first person to be convicted through the use of DNA evidence.


In addition to helping capture criminals, DNA testing has been instrumental in identifying human remains, such as in the Sept. 11, 2001, attacks, and in proving the innocence of some who have been falsely imprisoned. According to the Innocence Project, about 240 convictions have been overturned across the U.S. thanks to DNA testing. One such person is Kirk Bloodsworth, who was found guilty in a Baltimore court of sexually assaulting and murdering a young girl. In 1993, more than eight years after his arrest, DNA evidence compared to Bloodsworth's DNA did not match. In another case, DNA testing trumped a polygraph test that was used to convict four men of two murders in Chicago in May 1978. The men claimed they were innocent, but three failed a polygraph exam. The four men were convicted, and two were sentenced to death. The men spent 18 years in prison, but in 1996, DNA evidence proved their initial claim of innocence.


Since 1985, DNA evidence has dramatically changed the landscape of crime-fighting. According to the DNA Initiative website, "The development and expansion of databases that contain DNA profiles at the local, state, and national levels have greatly enhanced law enforcement's ability to solve cases with DNA. Convicted offender databases store hundreds of thousands of potential suspect DNA profiles, against which DNA profiles developed from crime scene evidence can be compared."


DNA testing doesn't lie, but it can, at times, be misleading as in the recent case of a mother who almost lost her children and was under suspicion because her DNA did not match that of her children. Further research showed that the DNA in her blood did not match the DNA in other parts of her body. The woman had a condition known as chimera---the merging of two nonidentical twins in the womb in a very early stage of development.

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