Wednesday, 25 January 2012 1:44pm

DNA: Unlocking crime's secrets

The potential of DNA technology to help identify or eliminate suspects, link multiple crime scenes and assist with the identification of victims has made DNA an invaluable resource for global law enforcement agencies, as well as the stuff of television crime shows.

While television highlights the drama and "magic" of DNA, in real life, the task of managing DNA evidence is based on correct procedures and quality assurance.

SAPOL's DNA Management Unit operates on a system of meticulous processing, thorough checking and accurate documentation. Bound by legislation to comply with the Criminal Law (Forensic Procedures) Act 2007, police adhere to a strict process of checks and balances with each and every sample.  

The Unit primarily works in two distinct areas: with DNA samples obtained by police from crime suspects and DNA retrieved from crime scenes.

DNA: part of the puzzle to unlock the secrets of serious crimes

In the area of DNA samples from suspects, police take a buccal (mouth) swab from any person suspected of committing a serious offence. These samples are checked in accordance with legislation and accuracy of supporting documentation. If there are any discrepancies, the sample is rejected and a fresh sample must be resubmitted.

When the sample makes it through the screening process, it is forwarded to Forensic Science SA (FSSA) for scientific testing and then entered on the South Australian DNA Database as a DNA profile.

In the area of DNA retrieved from crime scenes, specially trained crime scene investigators gather potential DNA evidence and submit them directly to the FSSA for examination.

If FSSA then advise that the DNA sample obtained from a crime scene is matched with an existing profile on the database, SAPOL's DNA Management Unit becomes involved.

The Unit completes further checks, before contacting the local area police Crime Management Unit to inform them that a positive DNA match result has been obtained.

Full details are then provided so local police can further their enquiries with the suspect.

Police emphasise that a positive match does not categorically mean a person has committed the crime; it only places the person at the crime scene at some stage.  It is then up to police using other investigative tools and skills to establish whether that presence was crucial to the case or purely circumstantial.

DNA technology will continue to grow as an important part of the police investigator's tool kit, joining fingerprinting, new and emerging technologies and traditional policing skills to create a crime busting force for our future, which can also reach back into the past to bring offenders to justice.

Key statistics

• 777: DNA matches received from FSSA and issued to local police for enquiry during 2010 – 2011 (linking crime scene samples to suspects on the database).
• 89, 472: Profiles held on the South Australian DNA database as at 30 November 2011.
• 602,000: Profiles (approximately) held on the National DNA database to the end of June 2011

 

DNA cold case scenario one

In the early 1990s, five 'stranger rapes' occurred across the metropolitan area of Adelaide.

These offences were all of a similar nature; the offender forced his way into the victims' homes, woke them, threatened them with a knife, and raped them.

Twenty years later, the arresting officer took a buccal swab from a man that was subsequently matched to DNA taken at the five rape crime scenes in the 1990s.

DNA cold case scenario two

In 2002 a woman who had been on a city bus tour passed out and woke up some time later believing she had been drugged and raped.

Police investigating a rape in 2010 arrested a suspect.  During the suspect's arrest, a buccal swab was taken, linking his DNA with that taken from other forensic items submitted.

The suspect's DNA was also linked to the rape that had occurred in the city in 2002, matching a sample that was collected from the victim at the time.