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

Case Study 84
An unknown offender broke into a house and stole several electrical appliances and some money. A cigarette
butt was left on the lounge room floor and was sent to the DNA laboratory for analysis. The laboratory advised
police that the DNA on the butt matched a profile on the DNA database. Police arrested and interviewed
this person, who alleged he was in prison when the offence was committed. After making inquiries with the
Department of Corrective Services, police confirmed that the suspect was in fact in custody at the time of the
offence. The suspect was released without charge. It is not known how the cigarette butt got there. 1155
There are many cases where police identify a suspect through DNA or other forensic evidence, but in the absence of
any other evidence implicating the suspect, the matter cannot proceed. The following case studies show how DNA
can link a person to a crime scene, but on its own cannot establish whether or not the person committed the offence.
Case Study 85
An unknown offender broke into a person’s garage and stole a number of cleaning products. A cigarette
butt found in the garage was analysed and linked to a suspect, who was subsequently interviewed. The
suspect denied any involvement in the offence. He explained that at the time of the offence he had been living
nearby with his parents, and often walked his dog in the park which backed onto the garage which had been
broken into. The suspect suggested that the butt may have blown or otherwise found its way into the garage.
Investigating police decided not to take any further action against the suspect. 1156
Case Study 86
An unknown offender broke into a house through the back kitchen window. Police officers attended, and took
fingerprints and a cigarette butt which had been left in the back yard. DNA on the butt was analysed and
linked to a person whose profile was on the database. The suspect was interviewed, denied any involvement
and offered no explanation as to why a cigarette butt with his DNA on it was found at the crime scene. Police
determined there was insufficient evidence to proceed. 1157
Police in the Northern Territory have conducted a number of “Genesweep” operations, which focus on identifying
property offenders through fingerprint and DNA analysis. The operations have reportedly resulted in a high number of
arrests, but many prosecutions have failed, because of the lack of other evidence. 1158 Even where there is insufficient
evidence to support a conviction, DNA links are still of intelligence value to investigating authorities, as they identify
possible offenders and enable police to better target their investigations.
The weight of DNA evidence may depend on the type and location of forensic material left at the crime scene.
Cigarette butts are a good source of DNA, because they usually have only one person’s DNA on them, but on its own,
a link between a suspect and a cigarette picked up at the crime scene is unlikely to establish the person committed
the offence. It may be more difficult to provide an innocent explanation for other types of forensic material found at
the crime scene, for example where a suspect’s blood is left on a broken window, or a suspect’s skin cells are found
under a victim’s fingernails. In conjunction with other evidence, a cigarette butt can still be used to convict, as the
following case study shows.
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NSW Ombudsman
DNA sampling and other forensic procedures conducted on suspects and volunteers under the Crimes (Forensic Procedures) Act 2000