It is called the CSI effect and it is being taken seriously by police officers and prosecutors across the country. Murderers are getting better at covering their tracks, by watching the hit television series CSI: Crime Scene Investigation, in which police forensics experts track down killers with state of the art equipment.
"It’s not uncommon for rapists now to bring bleach with them and effectively sanitize the crime scene," said Joshua Marquis, an Oregon prosecutor. Last year, Mr Marquis won manslaughter convictions against two women who had allowed an old woman in their care to die and then dumped her body into a ravine. In this case, however, watching CSI contributed to their downfall. "They were great fans of CSI … they were bragging to their friends that the police would never prove whether [the victim] had medication in her system, because she had been in the ravine for two weeks," Mr Marquis said. "They were just wrong."
Captain Ray Peavy, at the Los Angeles sheriff’s homicide bureau, told ABC television: "The ‘CSI’ factor is very definitely real. The criminals are learning what not to leave behind at crime scenes."
In Ohio, another CSI fan, Jermaine McKinney, has been charged with murdering a mother and daughter, then burning their bodies, using bleach to remove their blood from his hands, and lining his car with a blanket to avoid leaving traces. But he was given away by his ex-girlfriend.
Court papers said Mr McKinney, who "liked to watch CSI and other crime and forensic programs on television", was "concerned with the transferences of hair, sweat and DNA from him to the victim. This was why it was necessary for him to burn the bodies."
Prosecutors say more jurors have seen CSI and are increasingly reluctant to convict without hi-tech forensic proof.
"I can’t say we’ve seen a vast number of cases in which guilty people have walked free. But virtually every day prosecutors have to deal with it because a jury … expects DNA tests in every case, and in many cases there is no real DNA evidence," said Mr Marquis.