The Silent Witness

DNA on trial: can DNA evidence actually lead us to the truth?

Writer: Rupali Dabas
Editor: Kaya Kordelas


Accused of at least 13 murders, more than 50 rapes, and over 100 burglaries, the infamous “Golden State Killer” was finally apprehended after 45 years, based on a DNA profile recovered using a rape kit.

Detective Paul Holes, who oversaw the case, uploaded the murderer’s DNA profile into a personal genomics database called “GEDmatch” under a fake account. A large family tree was subsequently discovered from which two suspects were identified. To affirm their suspicions, a team of officers surreptitiously collected a DNA sample from the door handle of the suspect’s car. The sample was an exact match. On April 24th 2018, Joseph James DeAngelo was arrested, and initially accused of 13 accounts of first-degree murder.

The power of forensic DNA analysis is unquestionable – it is seen as the “gold standard” of crime scene evidence. Since Sir Alec Jeffreys’ innovation of genetic fingerprinting in 1984, DNA analysis has become a major focus of study for forensic scientists. It has played an irreplaceable role in the criminal justice community by facilitating the conviction of the guilty and exoneration of the innocent.

Since the 1980s, forensic DNA protocols have become faster, stronger, and increasingly accurate through the application of more sensitive technologies that enable greater access to the investigative potential of DNA testing. Forensic scientists now use single-nucleotide polymorphisms (SNPs) and short tandem repeat (STR) sequences in DNA profiling. These sequences represent highly variable regions that differ between individuals. And these differences, called polymorphisms, are inherited from our parents and are used to generate a DNA profile. As these sequences are only a few bases long, they are highly sensitive and allow the recovery of information from degraded DNA samples.

However, despite our greater understanding of the benefits of forensic DNA analysis, there are some problems associated with its use. Forensic scientists are becoming increasingly frustrated with the time taken for existing technologies to generate reliable DNA profiles. Sylvain Hubac, from the Forensic Science Laboratory of the French Gendarmerie (IRCGN), revealed that “the main goal today is obtaining a DNA result as quickly as possible…a mobile-DNA lab with fast and easy workflow can be very useful in obtaining DNA results in real time after collection”.

So, how close are we to achieving this goal?

Currently, it takes up to 72 hours for the police to receive a DNA profile from a crime scene, by which time the suspects have often been released. Keeping this in mind, a team of scientists at the University of Arizona developed “MiDAS”, a Miniaturised Integrated DNA Analysis System. This is a chip (no bigger than your hand!) that can extract, amplify, and analyse DNA. It only takes two hours to generate a complete DNA profile based on expert STR analysis! It can also process samples in parallel, which can be used to investigate multiple suspects.

Despite the numerous benefits of this technique, it is far from being integrated into current protocols that forensic scientists use in crime scene investigations (CSIs). This is because using such rapid-DNA techniques entails the risk of losing potential evidence, which is significant in cases where there is not much available. Hence, there might be no DNA left to be analysed by more trusted and existing techniques in forensic labs – this may let a criminal walk free! Using such rapid-DNA technologies may also generate less accurate results than the conventional techniques used in forensic laboratories. Therefore, despite the greater speed of DNA analysis offered by MiDAS, there is a need for more accuracy before it can be routinely used in CSIs.

Though DNA analysis is a key element in forensic analysis of crime scenes, contrary to popular belief, it is but a small part of discovering the truth behind a crime. Having blind faith in DNA evidence is dangerous and has led to wrongful incriminations of innocent people in the past – a topic that is seldom explored in popular crime shows.

In 2011, a woman was brutally raped in Plant Hill Park, Manchester. DNA evidence taken from the victim led the police to Adam Scott, who was promptly arrested. Upon questioning, he said that he’d been in Plymouth on that night, 200 miles away from the scene of crime. As no one could corroborate his claims, he was incarcerated. Scott spent five months in jail before it was discovered that the swab used to collect Scott’s DNA in an earlier incidence was accidentally re-used in the Manchester case. After further investigation into his phone records, he was liberated. Unfortunately, this isn’t an isolated case. Even now, the FBI is attempting to amend sentences delivered based on faulty DNA evidence.

Isn’t it astonishing then that we blindly trust the judgements of evidence based on something invisible to the naked eye? We must be aware of the incredible power DNA has to initiate a chain of events that could culminate in the conviction of an innocent person. For this reason, DNA alone is almost never enough to deliver a conviction. Powerful it may be, it still remains a silent witness.

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