A Basic Guide to DNA and the Criminal Law

Sep 6, 2023

The Queensland Crime and Corruption Commission has revealed that botched and flawed DNA testing at a specific forensic science centre over the past decade may have lead to hundreds of flawed prosecutions, resulting in potential wrongful convictions and acquittals. The investigation follows the failed prosecution of John Peros for the murder of his girlfriend, Shandee Blackburn, in which, the state-run forensic laboratory involved in the matter recorded 17 incorrect results in their DNA analysis.

What is DNA?

Deoxyribonucleic acid (DNA) is a molecule which is one of the basic building blocks of humans. It contains the information that determines the personal characteristics of each person. Nearly every cell in the human body contains DNA. DNA can be found in a person’s blood, semen, skin cells, tissue, organs, muscle, brain cells, bone, teeth, hair, saliva, mucus, perspiration, fingernails, urine, and faecal matter. Some cells, such as those found within saliva, are richer sources of DNA than other cells such as skin cells.

DNA is an important tool used by Police investigating criminal matters. There is however a lot of misconceptions about ‘DNA’ evidence and how it should be interpreted by lay people. This article will brush the surface on these issues and demonstrate why we need to be cautious when we use DNA evidence.

How are DNA examinations are done?

Typically, specialised Police Officers trained as Crime Scene Officers will attend a crime scene and examine for DNA evidence. This can include taking samples from body fluid such as blood and spit, or performing ‘tapelifts’ on surfaces and items.
These DNA profiles are then matched to those which are in possession of Police. Police and the Courts have powers under the Crimes (Forensic Procedures) Act 2000 to conduct forensic procedures on people to obtain DNA samples from them. This can range from the taking of blood, buccal (spit) samples, taking hair, and fingerprints.

The analysis of DNA samples and profiles is completed by scientists employed by the Forensic & Analytical Science Service (FASS). The scientists have expertise in the analysis of DNA and are able to comment on the different DNA profiles located from a source and the amount of DNA obtained. If there is an insufficient quantity of DNA, FASS may not deem there to be a match.

FASS scientists are not however able to comment on what body fluid/cell the DNA derived from or how the DNA got there.

Transference

An important concept in the examination of DNA is the concept of transference.
Transference is the idea that as we pass through the world we are constantly shedding our DNA by way of the depositing our cells. By shedding our DNA, other people and objects can then carry our DNA with them, and deposit them elsewhere. This is referred to technically as ‘secondary transfer.’

An example would be that person A goes to work with person B. The two work along side one another all day. Person B goes home, and they are subject to a home invasion and are killed. Crime Scene Officer perform an examination for DNA at the crime scene and locate person A’s DNA. It is a plausible explanation that person A did not murder person B, and that their DNA was just deposited on them throughout the day.

A more elaborate example would be if person B when he got home that evening hugged their partner, person C who then went for a run in a park and was killed, and person A’s DNA is located at the crime scene. It is a plausible explanation that person A’s DNA which was deposited on person B was passed onto person C when they hugged, and that he was not involved in their murder.

DNA as Evidence

These are just some of the complex issues and caveats associated with DNA evidence. From a legal perspective, DNA is treated as “circumstantial evidence.” Circumstantial evidence is not used to prove a fact directly, rather it is instead points to it being a possibility.

The strength of DNA evidence differs wildly from case to case. If a murder took place where a roommate or a partner’s DNA was located at the property, DNA evidence would have little if any value. Where if a body was located in the back of a car trunk, and a complete strangers DNA was located on the corpse, that DNA evidence would likely have more value.

It is for these reasons that Judges and Juries need to be wary of the “CSI effect” – the idea that DNA is an absolute way of determining guilt in a case.
DNA evidence and its treatment in the criminal law is a complex topic. Please do not hesitate to contact our office to discuss further.

Green & Associate Logo
Green & Associates

We are a community-focussed law firm based in Sydney’s Eastern Suburbs focused on results through practicality and simplicity.Since our inception in 2014, we have been driven by and focused on one thing only: to not only win our case or achieve our target, but to do it in the quickest, cheapest and most impressive way possible. Each and every one of our clients can expect that from us in every matter we undertake.We are committed to serving Sydney’s Eastern Suburbs through our criminal, commercial & personal practice areas.We believe everyone has the right to a second chance and the opportunity to make dreams a reality.

Green & Associates

We are a community-focussed law firm based in Sydney’s Eastern Suburbs focused on results through practicality and simplicity.Since our inception in 2014, we have been driven by and focused on one thing only: to not only win our case or achieve our target, but to do it in the quickest, cheapest and most impressive way possible. Each and every one of our clients can expect that from us in every matter we undertake.We are committed to serving Sydney’s Eastern Suburbs through our criminal, commercial & personal practice areas.We believe everyone has the right to a second chance and the opportunity to make dreams a reality.

MORE ARTICLES

NO BODY, NO CRIME? DEAD WRONG

NO BODY, NO CRIME? DEAD WRONG

NSW Police have charged former police officer Lamarre-Condon with two counts of murder after he allegedly killed Jesse Baird and his partner Luke...