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Introduction: What is DNA Fingerprinting?
With the exception of identical twins, everybody has a unique DNA genome. DNA is comprised of nucleotides, which are arranged in a specific order that represents the individual's one-of-a-kind genetic code. When DNA samples are collected from a crime scene, they are sent to a lab for DNA fingerprinting. DNA fingerprinting is a process in which forensic scientists use special proteins (restriction enzymes) to "cut up" DNA. The DNA is cut up into restriction fragment length polymorphisms, or RFLPs; their sizes, like DNA, are unique to each individual. This is what enables people trying to solve a crime to identify the perpetrators.
DNA fingerprinting history is full of interesting cases, and has piqued the interest of many in forensic science. This article will focus on three cases: Tommie Lee Andrews, the first criminal to be convicted in the U.S. with DNA evidence; Kirk Bloodsworth, the first person in U.S. to have death sentence overturned because of DNA evidence; and OJ Simpson, whose case is notable for the way in which it highlights the difficulty of contamination of samples.
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Tommie Lee Andrews: The First U.S. Conviction Based on DNA Evidence
Tommie Lee Andrews, a serial rapist, was the first criminal to be convicted in the U.S. with DNA fingerprinting evidence. The technology used to convict him was developed in the 1980s by British scientist Sir Alec Jeffreys, affiliated with the University of Leicester, and was used in 1986 to solve a case involving the strangulation of two teenage girls in a village near Leicester.
The judge at Andrew's first trial refused to allow DNA fingerprinting evidence, as he felt the science would confuse and mislead the jurors. This first trial ended in a mistrial. The judge at Andrew's second trial, however, did allow for DNA evidence, which resulted in Andrew's conviction in 1987.
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Kirk Bloodsworth: Conviction Overturned Based on DNA Evidence
In 1985, former Marine Kirk Bloodsworth was convicted and sentenced to death for the rape and murder of a nine year old girl named Dawn Hamilton. He received a second trial after a successful appeal based on the grounds of evidence having been withheld at his first trial. However, he was sentenced again, this time for two consecutive life terms.
After several years of fighting for a DNA test, samples from the scene of the crime were sent to a lab for tests. The final reports concluded that the DNA found at the scene of the crime did not match Bloodsworth's DNA, and he was released and pardoned by the Governor of Maryland shortly thereafter. Bloodsworth's ordeal lasted 9 years, including two years on death row. The DNA did match that of Kimberly Shay Ruffner, and on May 20, 2004, he pleaded guilty to the crime for which Bloodsworth was convicted.
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OJ Simpson: A Case of Contaminated DNA Samples
In the famous case of OJ Simpson, who was charged with murdering his ex-wife Nicole Brown Simpson and Ron Goldman, defense attorneys successfully made a case for cross-contamination of DNA samples due to poor handling procedures. In a nutshell, they argued that because the blood samples collected by the Los Angeles Police Department were taken with wet swatches and left in a hot truck for several hours, resulting in degradation. In addition, the defense also successfully argued that criminologists for the LAPD were, in general, poorly trained when it came to sample handling, did not follow standard protocol, did not take precautionary measures, and made serious errors when collecting samples.