What Is DNA?
DNA (deoxyribo-nucleic acid) contains individual genetic information about a person, who has the same DNA throughout the entire body located in every cell.
Where Can DNA Be Found at a Crime Scene?
Any residual material left from his/her body at a crime scene will contain that person’s DNA. Examples of bodily materials that contain DNA evidence include these: blood; saliva; hair; semen; mucus; fingernails; perspiration. A DNA sample is usually taken from a suspect by swabbing the inside of that person’s cheek. DNA evidence can be found just about anywhere at a crime scene, even on a victim. Typically DNA evidence may be found on such items as these: clothing; weapons; cups; toothbrushes; tissues; even in the injuries inflicted on the victim.
Nonetheless, although DNA evidence can be very accurate, there is sometimes the danger of that evidence being compromised (see below).
How Is DNA Collected at a Crime Scene?
DNA evidence can be easily contaminated during both its collection and its storage. This can occur when DNA evidence mixes with other persons’ DNA. Tellingly, this year the High Court unanimously allowed an appeal against the decision of the Full Court of the Supreme Court of South Australia and acquitted the appellant of murder. See, Fitzgerald v The Queen  HCA 28 (13 August 2014). Fitzgerald had been convicted of murder and causing serious injury as part of a group of six people involved in a home invasion that had taken place on the 19th June 2011. Fitzgerald claimed he was innocent, arguing that the DNA evidence found on a didgeridoo linking him to the offence had been transferred to his co-accused during a handshake earlier that evening. Hearing the appeal, the High Court held that the evidence was not sufficient to establish the prosecution case beyond reasonable doubt and that alternative hypotheses consistent with the appellant’s innocence had not been eliminated by the prosecution. The contentious issue was whether or not the appellant’s DNA, derived from his blood and found on a didgeridoo, was present because he had been at the scene of the crime with his co-accused, or whether the DNA had been present on account of a “secondary transfer” occasioned by an earlier handshake. Allowing the appeal, the High Court concluded that the prosecution had not established beyond reasonable doubt that the accused had been present at or participated in the attack.