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A forensic scientist analysing a blood sample.

How DNA analysis has revolutionised criminal justice

The discovery of deoxyribonucleic acid – more commonly known as DNA – is considered one of the most important discoveries of the 20th century. It’s not only been used to solve countless crimes, but exonerated people wrongly convicted, as well as solved several cold cases. The 1980 murder of Maria James in Thornbury – recently placed back in the spotlight thanks to the ABC’s Trace podcast – is an example of how re-examining DNA evidence in a cold case may finally lead to a result. The fact that this is possible – almost 40 years after the crime was committed – is quite extraordinary, and it’s thanks to significant inroads being made in DNA analysis technology over the past 30 years.

The evolution of DNA analysis

The very first discovery of DNA dates back to the late 1800s, when Swiss chemist Friedrich Miescher discovered what he called ‘nuclein’ – later named DNA – in white blood cells. But it wasn’t until the structure of DNA was solved in the 1950s that its potential was fully appreciated. Dr Annalisa Durdle, Lecturer in Forensic Biology at Deakin University, says that DNA analysis technology has come a long way since it was first used in a forensic context.

‘Today, DNA analysis technology is much more sensitive,’ says Dr Durdle. ‘DNA profiles can be obtained from single cells, whereas 30 years ago you would need large stains of biological material, such as blood or bodily fluid, to get a profile. Advances have also occurred in DNA collection techniques (swabs, tape etc.), implementation of DNA databases, a better understanding of the risks of contamination and developing labs to counter these risks, and better understanding of how DNA is transferred, etc.’

DNA analysis is now considered one of the most important and effective tools in forensic analysis and crime fighting.

The role of DNA in solving cold cases

Before DNA had ever been used in a forensic case, forward thinking law enforcement bodies, like Victoria Police, were hopeful that one day technology would become advanced enough that DNA stains collected at crime scenes could prove useful.

‘In 1982 Victoria Police made the decision to start storing biological material in a freezer,’ explains Dr Durdle. ‘In 2011 they started re-examining these pieces of evidence and solved a lot of cold cases through the DNA, particularly in sexual assault cases.’

This re-examination alone matched DNA profiles to more than 80 rapists in Victoria. Now, there are countless examples worldwide of DNA being used to solve crimes that occurred months, years and even decades ago. The ability to store DNA in national databases has also lead to perpetrators of crimes being caught who initially weren’t even considered suspects.

'In 1982 Victoria Police made the decision to start storing biological material in a freezer. In 2011 they started re-examining these pieces of evidence and solved a lot of cold cases through the DNA, particularly in sexual assault cases.'

Dr Annalisa Durdle,
Deakin University

DNA is nothing without thorough crime scene analysis

For DNA to be useful, proper crime scene management is essential. In the US, the case in which Amanda Knox was convicted (and ultimately cleared) of murdering her British roommate was found to have several issues with how evidence was handled. For example, a bra clasp – key DNA evidence in the case – was not collected for examination until six weeks after the murder and it was moved in the time between the murder and its eventual collection.

Dr Durdle says collecting all evidence at the crime scene as soon as possible after the crime has been committed is critical to overcoming issues such as this.

‘The more evidence you have, the more solid a case you can build,’ says Dr Durdle. ‘There is also the risk that if evidence is not collected, it may be lost. This can be due to environmental conditions (particularly if the crime scene is outside), people cleaning up, deliberate tampering by offenders or associates, having to reopen an area to the public etc. It is also important that evidence collected is probative. For example, if both the suspect and victim share a home, then collecting the suspect’s DNA from the scene may not be probative, as you would expect their DNA to be there anyway, and finding their DNA on commonly touched objects would not provide useful information to the investigators.’

Overcoming limitations of DNA

Over the years there have been some questions raised about the reliability of DNA evidence, particularly in terms of cross-contamination. While Dr Durdle says that some of these concerns are valid, contamination usually occurs due to external factors, rather than DNA itself being unreliable.

‘DNA is not necessarily the same “quality”,’ says Dr Durdle. ‘Some DNA may be exposed to environmental insults and therefore are degraded (moist environments that encourage bacterial growth, high UV, mixed up with dirt or inhibitors, for example). Also, you may collect a DNA sample but you have several donors so it is difficult to determine the individual profiles making up the overall sample.’

There have also been issues where DNA samples have been contaminated after being mixed up with others. For example, Melbourne man Farah Jama was wrongly convicted of rape in 2008 after a sample of his DNA contaminated a sample taken from the victim.

However, Dr Durdle says there’s been a lot of research conducted into overcoming contamination risk and, as a result, there are now several procedures in place that can mitigate these issues.

‘There are different kits available to analyse degraded samples, processes which remove inhibitors and software that can separate out different profiles (up to three people from the one sample at this stage). There’s also regular testing of lab equipment to check for background DNA; cross checking of lab records to ensure that if a DNA “match” is found, reference samples or other items from the case were not examined in the same lab at around the same time; and peer review of all work/documentation. As a direct result of the Jama case, sexual assault kits were introduced that contain all the items needed by the doctor for an examination so items are not taken from a pre-stocked trolley, and don’t run the risk of being contaminated by another person’s DNA.’

What’s next in DNA analysis technology?

Given that using DNA to solve crimes is a relatively new concept, there are several more developments to come that will improve DNA analysis and ensure it’s being used to its full potential. Currently, standard DNA analysis can compare DNA found at a crime scene to see if it matches with a suspect, but it doesn’t say much about a person’s appearance.

Dr Durdle believes that this is the area in which we will see the most significant advancement in the next few years.

‘Next generation sequencing will probably be the next advance in DNA analysis – this can look at larger parts of the genome and looks for single nucleotide differences in the DNA so it is much more discerning,’ says Dr Durdle. ‘You can also garner information about physical attributes of the donor, such as hair and eye colour, ethnicity etc.’

This could result in a computerised 3D genome recreation of a person – that is, a picture of a suspect. Dr Durdle also says there will be improvements in the efficiency of processing DNA.

‘New technology will also be focused on getting profiles faster, cheaper and possibly in the field. There have already been developments in this direction.’

Interested in learning more about DNA and crime scene analysis? Consider studying forensic science at Deakin.

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Dr Annalisa Durdle
Dr Annalisa Durdle

Lecturer in Forensic Biology, Faculty of Science, Engineering and Built Environment, Deakin University
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