What is DNA profiling?
DNA profiling (also termed DNA fingerprinting) is a procedure that aims to develop a DNA profile for a person by obtaining a unique DNA pattern from them. With over 99.1% of the DNA in the human genome shared by all humans, the variability in the remaining 0.9% of our DNA sequences can be used by scientists to distinguish individuals. DNA profiling and advances in forensic technology have proved critical in identifying relationships between people (as in the case of paternity tests), identifying perpetrators (as in the case of most sexual assault cases), and exonerating victims.
DNA can be collected in various forms, from skin tissue and hair follicles to bodily fluids like blood, saliva, urine, semen, and sweat. When working to identify perpetrators, a suspect’s DNA profile is screened against the FBI’s CODIS, or Combined DNA Index System – a database of all DNA profiled contributed to by the state, federal government, and forensic labs, first established in the 1990s. More recently, investigators team up with private companies and genetic genealogists to expand their database to people who have voluntarily provided their DNA to discover relatives and ancestors. Before CODIS, DNA samples collected from the crime scene often just sat there. In crime, DNA is now used in cases of property crime to murder.
How has it been used to confirm perpetrators?
The earliest case of DNA evidence being used in an investigation was in the rape and murder cases of Lynda Mann and Dawn Ashworth, who were both 15 and the time they were attacked. Although their cases were 2 and a half years apart, police suspected their attacks to be the work of a serial killer and began their hunt. Just 2 years prior to Dawn Ashworth’s case in 1986, Alec Jefferys had revolutionized the world of forensic science with his development of genetic fingerprinting. Police decided to apply these new techniques in their new case – after semen was collected from the dead bodies of both girls, police set their first suspect, in custody for more than 3 months, free. They then decided to examine blood samples from every man in the neighborhood where the girls were killed.
One of the men who allegedly gave a blood sample was a man named Colin Pitchfork. His sample had not been a match, but later police were informed that he was impersonated by a man named Kelly, who had also taken the blood test on his behalf. When the real Pitchfork was arrested and his samples analyzed, they turned out to be a match to those from the crime scene. Pitchfork was convicted and sentenced to life in prison in January 1988.
By the turn of the century, DNA was already closing the cases of violent crimes. City Journal provides examples of some striking cases after the first success investigators in the US had with DNA testing in 1987. In 1987, crime labs made positive matches to serial rapist Tommy Lee Andrew’s samples and the blood and semen found at his latest victim’s home, and stories of successes with DNA came not long after. In the mid-1990s, a rape victim was confident Robert Flowers was her attacker as she was sure she had seen him on the street. After Flowers maintained his innocence, DNA evidence showed that the perpetrator was in fact, his brother. DNA has proved remarkable in identifying familiar relationships but in several, differentiating family members – even in the case of identical twins.
DNA evidence has proven especially useful in sexual assault cases, where DNA is collected from the victim’s body and clothes and also at the scene of assault when possible, where other bodily fluids might be present. In 1998, a 12-year-old girl informed police that she was being sexually abused by her grandfather; “after watching an NYPD Blue episode in which a rape victim saved the semen her attacker had left behind, the young girl, using a cotton swab on herself, gathered sufficient DNA evidence to have her grandfather arrested.” (City Journal)
DNA samples have also been obtained through indirect means when suspects won’t comply. In 1998, serial rapist and robber Charles Peterson was suspected by the police, one of whom eventually followed him after he refused to give a DNA sample for comparison for the cases. As he trailed Peterson in his car, the officer carefully collected saliva from the ground where Peterson on his motorcycle had just spit on while stopped at the traffic light. The saliva proved a match and Peterson was arrested.
In several other cases, DNA evidence was obtained from a relative of the perpetrator, when there was only a partial positive match to the relative.
In 2014, the daughter of a man named Christopher Hampton was involved in a domestic violence incident, and per police protocol, samples of her DNA were gathered. The next year, DNA testing was rerun for the rape and murder of Melanie Road, which occurred over 30 years prior. After Hampton’s daughter proved to be somewhat of a match, Hampton was then asked to provide DNA. His sample proved to be a match to the bodily fluids found on Road’s body at the time and he was arrested.
Finally, not all evidence used to confirm perpetrators has been obtained from humans. In 1993, the first case of “genetic testing of botanical life,” two tree seed pods found in the bed of a man named Mark Allen Bogan were matched to a palo verde tree at the murder site of a woman a year prior. This directly linked Bogan to the crime because he had insisted he had never been near the site, even after his pager was found on the body. However, plant genetics prove much harder to test for, with the palo verde tree DNA patterns around “15 times more complex than those for humans” and the geneticist on the case noting that he had spent “at least 100 hours analyzing the palo verde DNA.” As seen here, plant genetic evidence, even down to pollen specs, is most commonly analyzed to link people – whether suspect or victim – to places. (AP)
Sources:
https://www.rainn.org/articles/importance-dna-sexual-assault-cases
https://online.maryville.edu/blog/how-is-dna-profiling-used-to-solve-crimes/
https://cen.acs.org/analytical-chemistry/Thirty-years-DNA-forensics-DNA/95/i37
https://apnews.com/article/326da16edd9e677ce6033700e470e9ae
https://www.city-journal.org/html/dna-testing-next-big-crime-busting-breakthrough-11755.html
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