单项选择题

Violent criminals with something to hide have more reason than ever to be paranoid about a tap on the shoulder which could send them to jail. Queensland police are working through a backlog of unsolved murders with some dramatic success. Greater cooperation between the public and various law enforcement agencies is playing a role, but new genetic-testing techniques are the real key to providing the vital evidence to mount a prosecution.
Evidence left behind at the scene of any murder is guaranteed to outlive the person who left it. A blood, saliva or tissue sample in the size of a pin, kept dry and out of sunlight, will last several thousand years. From it, scientific analysis now can tell accurately the sex of the person who left it.
When matched against a sample from a crime suspect, it can indicate with million-to-one certainty whether the samples come from the same source. Only twins share identical DNA. So precise is the technology if the biological parents of a suspect agree to provide a sample, forensic scientists can work out the rest for themselves without cooperation from the suspect.
Queensland forensic scientists have been using the DNA testing technology since 1992, and last year they were recognized internationally for their competence in positive individual identification. That is part of the reason 20 of Queensland’s most puzzling unsolved murders dating to 1932 are being ac timely investigated. There also have been several recent arrests for unsolved murders.
Forensic evidence was instrumental in charges being laid over the bashing death of waitress Tasha Douty on Brampton Island in 1983. Douty’s blood-splattered, naked body was found on a nude sunbathing beach at Dinghy Bay on the island. Footprints in the sand indicated that the killer had grappled with the 21-year-old mother who had fled up the beach before being caught and beaten to death.
According to Leo Freney, the supervising forensic scientist at the John Tonge Centre at Brisbane’s Griffith University, DNA testing has become an invaluable tool for police, its use is in identifying and rejecting suspects. In fact, he says, it eliminates more people than it convicts.
" It is easily as good as fingerprints for the purpose of identification, " he says. "In the case of violent crime it is better than fingerprints. You can’t innocently explain things like blood and semen at a crime scene where you may be able to innocently explain fingerprints. " In Queensland, a person who has been arrested on suspicion of an offence can be taken before a magistrate and ordered to provide a sample of body fluid by :force if necessary.

Evidence left behind at the scene of a crime is all of the following EXCEPT（）

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