Crimes (Forensic Procedures) Act 2000 - NSW Ombudsman - NSW ...

Case Study 76
A man was arrested and charged in November 2002 for the murder of Karen Allen in Dapto, after his
DNA profile was found to match a profile derived from forensic material found on the deceased’s bra.
The defendant argued that his DNA was found on her bra as a result of secondary transfer – that although
he had no recollection of having met the deceased, he may have met her at some point on the night she was
murdered, and some of his skin cells may have come into contact with her clothes. The defendant was found
not guilty. The murder investigation is now focusing on other evidence, including a DNA profile obtained from
the deceased’s trousers. It is not known who this second DNA sample came from, but it did not come from
the defendant. 1099
Nothing can really be done to minimise adventitious transfer, it is simply a product of our daily lives and the capability
of analysis techniques to identify smaller and smaller traces of DNA. However, the possibility of adventitious transfer
again highlights the need for investigating police to pursue other investigative strategies in addition to any forensic
analysis. Many of the police officers we surveyed made this point – that DNA analysis, while effective in many cases,
is only one of a number of tools available to them in the investigation and prosecution of crime.
12.2. Contamination by police officers and other evidence gatherers
The term ‘cross contamination’ generally describes the transfer of DNA at some point after a crime has been
committed. It can occur at any stage of the investigation, from the time the crime scene is first examined; during the
transportation or storage of exhibits; or during analysis at the laboratory. Contamination by police officers can occur
during a forensic procedure, or during the police handling of crime scene evidence. 1100
Again, the increasing sensitivity of DNA analysis techniques means that there is a greater chance of detecting DNA
from more than one person on crime scene evidence. Given that a profile can now be derived from a very small
amount of DNA, there is an even greater need for safeguards against the risks of cross contamination by those
involved in the investigation of the crime.
12.2.1. Contamination of person samples
The DNA sampling system is designed to minimise contamination. Sampling kits are distributed to police stations in
tamper evident bags. The kit contains everything which is needed for the procedure, including rubber gloves, which
the police officer puts on before taking the sample. Where the DNA sample is taken by buccal swab, the officer opens
the swab packet, and instructs the person providing the sample to take the swab out of the packet. After the person
has finished taking the saliva sample, the officer should handle only the stem of the swab. The FTA card is folded up,
sealed with an adhesive barcode and put in an envelope which is then sealed with another barcode. In the case of
hair samples, the hairs are put in an envelope, which is sealed with a barcode. The envelope containing the FTA card
or hairs is then put in a second tamper evident bag, which is sealed in the presence of the suspect, and sent to the
laboratory for analysis.
Contamination may also be an issue in forensic procedures other than DNA samples, for example in nail scrapings,
swabs from the body and gun shot residue tests. These types of procedures are conducted by specialist forensic
officers, rather than general duties police officers. These officers are trained to minimise contamination risks, for
example by wearing protective clothing. Where a procedure involves taking forensic material other than the person’s
own DNA, police may also take measures to prevent contamination, such as asking a suspect to wear gloves while
waiting for a hand swab or nail scraping to be taken.
The requirement that forensic procedures be electronically recorded also provides protection, for both police and the
person providing the sample, against allegations of contamination.
During our video audit, we reviewed the forensic procedures we watched for any observable contamination
risks during the sampling process. We found that officers generally took appropriate steps to minimise the risk
of contamination. Some took additional steps, for example by cleaning the testing table with disinfectant before
conducting the procedure. However, in 13 (or 9 per cent) of the videos we watched, we had concerns about possible
contamination.
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NSW Ombudsman
DNA sampling and other forensic procedures conducted on suspects and volunteers under the Crimes (Forensic Procedures) Act 2000