A Short History of DNA profiling

A prosecutor has over 70 witnesses against a defendant in a murder trial, yet the Jury pronounced him not guilty? Why was this? The Jury say it’s because there was no proof he had the gun, no blood spatter, no DNA.

Image 1: The CSI effect now affects juries.
Credit: © ProjectManhattan / Wikimedia Commons / CC-BY-SA-3.0
imag

They wanted hard evidence on which to base their decision (Dakss, 2005). Popular culture calls this the CSI effect, based on the popular television show (The Crime Museum, 2022).  The hardest of hard evidence is considered to be DNA. How did this happen? It’s been nearly 40 years since DNA first played a part in criminal investigation.  Let’s look at a short history of DNA profiling.

What is DNA profiling?

When examining  DNA, the scientist studies non-coding DNA. These areas used to be termed ‘junk’ DNA, before researchers understood more about its function.  The technique looks for repeated nucleotide sequences, known as Short Tandem Repeats (STR), at specific points in the non-coding DNA, called gene loci (Science Learning Hub, 2016). Between different individuals, the loci are not always present in the same area of the genome. Looking at only one loci in the DNA, a similarity in position between two people is not that unusual. However, when examining 15 or 16 loci then two people are unlikely to have their STRs in the same loci position. If two samples achieve the same results then there is more certainty of a match. In the US, the FBI, use 20 core loci to determine match probabilities (FBI.gov).

Of course, in the general population some of the STRs at loci are rarer than others  making the probability of a match higher. Complex mathematics are used to determine the likelihood of a match between samples. The more loci used in a match probability, the more complicated the mathematics for the Random Match Probability (RMP) becomes (Perlin, 2017).

History of DNA profiling

As I said above, it has been about 40 years since DNA was first used in a police investigation. In the beginning, DNA profiling was performed exclusively on blood. More recent cases have involved other bodily fluids and bone fragments  (easy DNA, 2022).

Profiles produced 40 years ago, were nothing like the polished results presented as court  cases in 2023. In 1985, Professor Alec Jeffries presented a paper discussing his team’s work on comparing  short sequences of DNA from various animals to human DNA (Saad, 2005). In the beginning, DNA profiling used fragments of DNA that could be hundreds of base pairs long, called Variable Number Tandem Repeats (VNTR).  Because of this, it could take weeks to test DNA for a profile using an x-ray based, gel electrophoresis system. During the 1990s, scientist switched to smaller fragment, STR analysis, which uses capillary electrophoresis, separating DNA fragments by size, and using fluorescence detectors. This decreased the time required to produce a profile (Arnaud, 2017).

The addition of Polymerase Chain Reaction (PCR) to the toolkit of Forensic DNA Profiling, meant that even small samples of DNA provide the police with clues that help them find an offender (Caister).

Databases for DNA Profiles

What was needed was the ability to save and compare these generated profiles. DNA profiles can be stored in computer Databases similar to those of fingerprints and footwear marks. (https://mozartcultures.com/en/fingerprints-vs-fingermarks/   and https://mozartcultures.com/en/footwear-marks-in-solving-crime/ ). Using these,  crimes can be linked across countries and across the world (Interpol).  US law enforcement agencies use CODIS (Combined DNA Index System) to record profiles from convicted offenders.  In one case, a match from this database prevent the release of a rapist who was about to be released on parole (Panneerchelvam, 2003).

Ancestry Searches from DNA Profiles

Part of Jeffrey’s work showed the repeating sequences in a child’s DNA was not identical to either parent, but a mixture of the two. He announced that the technique might solve paternity disputes (Saad, 2005).

Paternal DNA, in the form of the Y chromosome, is very useful in tracing the male line. The STRs on the Y chromosome are preserved from mutation, in the same way as other STRs.

Image 2: Paternity testing.
credit: https://commons.wikimedia.org/wiki/File:DNA_paternity_testing.svg

The Y chromosome passes on from father to son to grandchild virtually unchanged, making ancestry tracing easier. It is also useful in rape cases, to distinguish low levels of male DNA from larger amounts of the victim’s DNA (Daeid, 2021).

For Maternal lineages, DNA from the mitochondria can be used effectively. Mitochondria are found in cell cytoplasm, and are inherited solely from the mother (Chadwick 2023).

DNA identification, along with dental records, is also useful in identifying victims of natural disasters (Bowman, 2022). However, DNA profiling has also proved a versatile tool to aid the police in a variety of criminal cases.

Case Study 1- DNA Profile of a Murderer

In the UK in 1983, the body of 15-year old Linda Mann was found on a lonely path, raped and strangled. Three years later, Dawn Ashworth was found nearby with similar injuries. The police obtained a confession to the second crime, from Richard Buckland, but the man was unclear on the details. Professor Alec Jefferies, mentioned above, was asked to perform a profile on semen found on the two girls. These tests cleared Buckland. With the data from the DNA profile, the police asked all local men to provide a voluntary sample for testing.  They found no one, but later a man admitted that he had provided a sample for his friend Colin Pitchfork. Pitchfork was arrested and confessed to the murders.  This case proved that DNA testing was not just about paternity identification, now the technique proved useful in criminal cases (Butler, 2010).

Case Study 2 – DNA Profile of False Identity

Anna Anderson claim throughout her life to be Anastacia, the missing daughter of the executed Czar Nicholas II of Russia. She died in 1984, before DNA testing found a proper niche, and was cremated as per her wish.  However in 1994, two teams of scientists worked with preserved tissue samples, one of blood and one of small intestine. When compared with the exhumed remains of the Romanov’s, neither team found any similarity in the DNA. It is believed that Anna Anderson was the daughter of a Polish farming family, who hoped to improve her life. She fell into the deception after a stay in a psychiatric hospital (Fowler, 1994).

Case Study 3 – DNA Profile of a Rapist

In 1987, a man broke into a Florida home and raped a woman. The main suspect, Tommy Lee Andrews, swore that he had been at home that evening, without witnesses to prove otherwise this was a statement difficult for the police to disprove. However, there was a new test in town that year. As DNA evidence had successfully acquitted a man in the UK for murder, the police sent Andrews DNA for testing. A sample of Andrews blood was analysed  along with semen evidence from the crime scene. With the results, the police were able to confidently state that Andrews was the criminal. With additional identification from his victim and the DNA evidence, he was sentenced to 22 years in prison. The first person in the US to be convicted on the basis of DNA profiling evidence (Crenson, 1997).

Obstacles in acceptance of DNA profiling

Of course, it wasn’t going to be easy convincing the courts to accept a new form of evidence. No one develops a new test in forensic science without lawyers casting doubt on the viability of the technique. Scientific method applied to cases before a court of law is the very definition of Forensic Science, therefore the scientists running DNA analysis must prove that DNA is as individual as fingerprints (National Research Council, 1996). DNA profiling is based on mathematical statistics, therefore there is always an element of doubt in any profile offered to a court.  Prominent cases where evidence has been mishandled have led to stringent rules on the collection of evidence so that it can be used in a court of law.

Case Study 4 – Flawed Collection

Italian police were called to investigate the death of Meredith Kercher in 2011. They arrested her flatmate Amanda Knox on the basis that her DNA was discovered on a kitchen knife they decided was the murder weapon.

Image 3: Amanda Knox is released from custody, vindicated.
credit: https://commons.wikimedia.org/wiki/File:Corrado_maria_daclon_-_amanda_knox.jpg

Videos and photographs of the crime scene, showed the investigators not using basic anti-contamination techniques such as gloves or hair caps. Clothing, used as evidence, was moved from its original position before collection 46 days later. Many other worrying failures of proper investigation allowed the eventual exoneration of Knox( Injustice Anywhere, 2012).

Case Study 5 – Evidence Tampering

The 1994 US case of OJ Simpson is possibly the most notorious for highlighting failures of investigation and evidence collection.  Simpson was accused of murdering Ron Goldman and his ex-wife, Nicole Brown. He was acquitted. During the trial, evidence showed severe deficiencies in the correct collection procedures. Samples, such as a vial of Simpson’s blood, had simply gone missing.  Further representation held the possibility that evidence had been planted on the crime scene. This case became the prime example of how not to conduct an investigation (Forensic Colleges, 2023).

Finally

As with all new techniques in Forensic Science, DNA profiling has had to prove its utility in helping police solve crime. The problems of cross-contamination and  poor chain of custody are present in all areas of forensic investigation, but with DNA being so valued by the jury, then it is vital that collection is highly regulated. While it is a powerful tool, without correctly documented collection, DNA profile evidence is worthless.  Forensic investigators have learned important lessons from these failures and successes to ensure that DNA profiling provides the best evidence in a Court of Law.

References

Arnaud, C.H. (2017) Thirty Years of DNA Forensics: How DNA has revolutionized criminal investigations. Chemical and Engineering News. Vol 95. Iss 37. September 18. https://cen.acs.org/analytical-chemistry/Thirty-years-DNA-forensics-DNA/95/i37

Bowman, Z., Daniel, R., Gerostamoulos, D., Woodford, N.,  and Hartman, D. (2022) Rapid DNA from a disaster victim identification perspective: Is it a game changer? Forensic Science International: Genetics. Volume 58, https://doi.org/10.1016/j.fsigen.2022.102684

Butler, J. M. (2010) Fundamentals of Forensic DNA Typing. London: Academic Press. https://aboutforensics.co.uk/colin-pitchfork/

Caister Academic Press. PCR in Forensic Science. https://www.caister.com/highveld/pcr/pcr-forensic-science.html#:~:text=PCR%20can%20be%20used%20as,compared%20with%20a%20DNA%20database

Chadwick, L.H., (2023) Mitochondrial DNA. National Human Genome Research Institute. February 23. https://www.genome.gov/genetics-glossary/Mitochondrial-DNA#:~:text=Mitochondrial%20DNA%20is%20the%20circular,mitochondrial%20DNA%20—%20from%20their%20mother

The Crime Museum. (2022)The CSI Effect. https://www.crimemuseum.org/crime-library/forensic-investigation/the-csi-effect/

Crenson, M. (1997) Serial Rapists Conviction was First to Involve DNA. Los Angeles Times. March 2. https://www.latimes.com/archives/la-xpm-1997-03-02-me-33996-story.html

Daeid,N.N, Hackman, L., and Court, D.S. (2021) The Y chromosome and its use in forensic DNA analysis. Emerg Top Life Sci. 24 September. 5 (3): 427–441. doi: https://doi.org/10.1042/ETLS20200339

Dakss, B. (2005) The CSI Affect. CBS News. https://www.cbsnews.com/news/the-csi-effect/

Easy DNA. (2022) A History of Forensic DNA Analysis. https://easydna.co.uk/knowledge-base/history-of-forensic-dna-analysis/#

FBI.gov. Frequently asked Questions on CODIS and NDIS. https://www.fbi.gov/how-we-can-help-you/dna-fingerprint-act-of-2005-expungement-policy/codis-and-ndis-fact-sheet

Forensic Colleges. (2023) Fraud in Forensics: Five Cases of Abuse and Evidence Mishandling. https://www.forensicscolleges.com/blog/resources/real-cases-of-forensic-fraud-flawed-evidence

Fowler, R.J., (1994) Anastacia: The Mystery Resolved. The Washington Post. October 6. https://www.washingtonpost.com/archive/lifestyle/1994/10/06/anastasia-the-mystery-resolved/f208f264-a141-4f54-8354-934a3005f091/

Injustice Anywhere. (2012) Amanda Knox: The Uncollected Evidence. Video. https://www.youtube.com/watch?v=tYJiZq3TQh0&t=73s

Interpol. (2023) DNA. https://www.interpol.int/en/How-we-work/Forensics/DNA

National Research Council (US) (1996) Committee on DNA Forensic Science: An Update. Washington (DC): National Academies Press (US); https://www.ncbi.nlm.nih.gov/books/NBK232607/

Panneerchelvam, S., & Norazmi, M. N. (2003). Forensic DNA profiling and database. The Malaysian journal of medical sciences : MJMS, 10(2), 20–26. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3561883/#:~:text=DNA%20fingerprinting%20was%20first%20used,had%20not%20committed%20the%20crimes

Perlin, M.W. (2017). Forensic match information: exact calculation and applications. International Conference on Forensic Inference and Statistics, Minneapolis, MN, 7-Sep. https://www.cybgen.com/information/presentations/2017/ICFIS/Perlin-Forensic-match-information-exact-calculation-and-applications/page.shtml

Saad R. (2005). Discovery, development, and current applications of DNA identity testing. Proceedings (Baylor University. Medical Center), 18(2), 130–133. https://doi.org/10.1080/08998280.2005.11928051

Science Learning Hub – Pokapū Akoranga Pūtaiao. (2016) DNA Profiling. https://www.sciencelearn.org.nz/resources/1980-dna-profiling