Fingerprinting: Genes and Justice

Since genetic fingerprinting was discovered 37 years ago, genetics has become a breakthrough tool used in the justice system; from victim identification, to suspect detection, to assisting in prosecution, genetics is an integral part of criminal investigations. But how does forensic genetics work?

A copy of our DNA is in almost every single cell of our body, around 30 trillion cells. Throughout the day, you are constantly shedding these cells, essentially leaving a trail of DNA behind you. Although some of our DNA makes up our genes, which act as an instruction manual for the body, there are large sections of DNA, called Short Tandem Repeats (STR), which do not act as instruction for anything at all. Sections of STRs vary in size, and as half of your STRs are inherited from your mum, and half are inherited from your dad, the sections of STR and the length of these sections, varies from person to person. It is these different lengths which tag your DNA as being distinct to you. If two pieces of DNA are compared, the more STRs they have of the same size, the more closely related they are.

If all the STR are the same size, then the two DNA samples are a genetic match (and therefore from the same person). This is called genetic fingerprinting.  This is one of the ways law enforcement use DNA to determine whether a suspect is the person who participated in a crime, by matching DNA left at the crime scene and comparing it to the DNA of the suspect.

The first-time forensic genetics was used, was on a case in the 1980s in England. On the 1st of November 1983, Linda Mann, a 15-year-old girl from a village in Leicestershire, left a neighbour’s home after babysitting, but never returned home.  Her body was found the next morning. The young girl had been brutally raped and strangled, but despite Police Officers’ best efforts, no leads or suspects were uncovered, and the case was left to go cold. Three years later, on the 31st of July 1986, Dawn Ashworth, another 15-year-old girl from the same village, left her home to visit a friend, but never arrived. Her body was found two days later. Again, Ashworth had been brutally raped and strangled.

Officers believed that both murders had been committed by the same person. Thankfully, this time, a suspect emerged; Richard Buckland, a 17-year-old boy was arrested by Police, and later confessed to the murder or Dawn Ashworth. However, Buckland didn’t admit to the murder of Linda Mann. Convinced that the two crimes were linked, the Police recruited the help of Professor Alec Jeffreys, to tie Buckland to the first murder. Jeffreys had discovered genetic fingerprinting in 1984.

However, when comparing the DNA at the crime scenes, the DNA profiles of the killer and Buckland didn’t match for either crime meaning…he didn’t do it. And so started the first genetic manhunt to find a DNA match with the real killer’s profile. 480 men in the Leicestershire village gave their blood for comparison, but still no matches were found. Until, one night, a man was overheard telling a friend, that he had taken the blood test in place of a workmate. Based on this tip, a 22-year-old man, Colin Pitchfork was arrested, and his DNA was compared to the DNA at the crime scenes. It was a match.

Although this initial case of genetic fingerprinting proved the incredible influence of forensic genetics, it was still a relatively small-scale case. Around the same time, a notorious serial killer, serial rapist, and burglar had been rampaging through California from 1973 to 1986. A detailed and extensive genetic profile had been created for the unknown subject, linking him to at least 13 murders, 50 rapes, and 120 burglaries; unfortunately, no leads were found, and the case went cold. The DNA left at the crime scenes didn’t match anyone in the criminal database, and, unlike the village in Leicestershire, it would have been a significantly larger exercise to obtain DNA from every man in California, and so, it became unlikely that the crimes would be solved using DNA.

However, with the increase in direct-to-consumer genetics, whereby the public sends their DNA to private genetics companies, the FBI realised that there was a wealth of untapped genetic information available. Many years after the crimes, the FBI uploaded the DNA of the killer into the database of a private genealogy company, which enables people to track long-lost relatives and ancestors. Using this database, the FBI were able to identify a cousin of the suspect. On 25th April 2018, 72-year-old Joseph James DeAngelo was identified as the Golden State Killer and on 21st August 2020, DeAngelo was sentenced to life imprisonment without the possibility of parole. A 40-year-old cold case, cracked with the help of genetics.

Although forensic genetics has proven to be vital in law enforcement and conviction, there are some issues that need to be accounted for; the use of direct-to-consumer genetics companies by law enforcement has repeatedly received backlash. A major issue with using these databases, is privacy. Although an individual must give consent to a company to retain their genetic information, this one person’s DNA can be used to identify hundreds to thousands of genetic relatives. The implications to so many other people, who have not themselves given their consent, puts these peoples’ privacy at risk.

Furthermore, forensic genetics is not infallible, and can, in some cases, lead to wrongful arrest. One such example is the case of Adam Scott, who was arrested on suspicion of rape in 2011, despite claiming he had been hundreds of miles away at the time. Months later, phone records placed Scott in Exeter at the time of the crime, corroborating his story. It was found that the DNA evidence used to implicate Scott was present due to accidental contamination. A plastic tray containing a sample of Scott’s DNA was mistakenly re-used to analyse the swab from the victim’s rape-kit. Therefore, although forensic genetics has been shown to be an important key in suspect identification, it should only be used as an investigative tool in the wider context of evidence.

Overall, forensic genetics has been used worldwide to catch criminals, who may otherwise be left at large. It has not only been used to crack decade old cold cases but has also in daily police work to identify victims, narrow down suspect lists and assist in prosecution. Although great care needs to be taken with the ethical implications of using direct-to-consumer genetics databases, and even considering human errors associated with forensic genetics, it is undeniably a vital tool in the fight against crime.

References

https://www.bbc.co.uk/news/world-us-canada-57947785

https://www.bbc.co.uk/news/world-us-canada-43915187

https://www.bbc.co.uk/sounds/play/p09sp57z

https://senseaboutscience.org/wp-content/uploads/2017/01/making-sense-of-forensic-genetics.pdf

https://www.thelancet.com/journals/lancet/article/PIIS0140-6736%2804%2917621-6/fulltext

https://le.ac.uk/dna-fingerprinting/explained

https://customwritings.co/murder-of-lynda-mann-and-dawn-ashworth/

https://www.thesun.co.uk/news/15190933/colin-pitchfork-killer-rapist-free-dna-fingerprinting/

http://www.biology.arizona.edu/human_bio/activities/blackett2/str_description.html

 

Disclaimer

The information in this blog is for information and entertainment purposes only. I am not a medical professional, so I have never and will never give medical advice in this blog. You should always speak to a healthcare professional about your unique health needs. My opinions are entirely my own and do not reflect the organisations or people I work for. I only discuss published literature in this blog which are referenced with links.

 

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