Expert warns of ‘decoy’ DNA profiles

Super-sensitive methods of DNA detection, such as low copy number (LCN), open the door to criminals creating decoy profiles by simply obtaining the DNA from anyone by a number of means and placing it at the scene, a leading forensic expert has warned.

“A criminal could easily collect tens of cigarette butts and ‘litter’ a crime scene with the many DNA profiles that officers would find on the discarded cigarette ends,” said Professor Alan Jamieson, director of the Forensic Science Society.

Alternatively, added Prof Jamieson, a burglar may camouflage a single item of evidence that has been in contact with a known offender at the crime scene. Any person who has been arrested in the past would have their DNA profile stored on a national database and be known to the police, making them an ideal person to ‘frame’ for a crime.

“There may be cases going to court where individuals who have committed crime in the past – whose DNA profile is known to police – may have been framed by another individual,” said Prof Jamieson.

“A single cigarette butt left at a crime scene could be considered vital evidence by the police.”

The problem is, he added, that it is not known if any cases where decoy profiles have been planted, have actually led to a prosecution. “How would we actually know?” he said.

“What I do know,” he added, “is that in a number of cases DNA obtained from a cigarette butt can be considered enough evidence to form a case against a suspect.”

He said one problem is the presumption that DNA equals guilt. “Although the Association of Chief Police Officers (ACPO) claims the police do not prosecute on the basis of DNA alone, I know that is not true.”

Prof Jamieson said that although there is a consensus that DNA evidence alone can be used to prosecute in a sexual assault case, for example, where it proves physical contact was made against a victim if the suspect claims no contact was made, the same rule should not apply for other offences such as burglary.

“For volume crime offences, such as breaking and entering, officers must proceed down more avenues of investigation if they have only DNA evidence to go on; that is only one piece of the jigsaw.

“When you don’t have a known body fluid of the suspect then you can’t prove he/she was at the crime scene solely on DNA evidence.

“Bloodstains, for example, are much stronger evidence when placing a suspect at a crime scene compared to a DNA profile obtained from skin cells, which super-sensitive techniques obtained DNA profiles from.”

Prof Jamieson said ever since the birth of fingerprint evidence criminals have become aware of the forensic capabilities practiced by police and crime scene investigators.

“They are much more aware now of DNA evidence and leaving decoy profiles at a crime scene could be a tactic soon deployed by criminals and it may have already occurred in a fraction of cases.”

Prof Jamieson was accused by another leading forensic scientist of being “irresponsible” and “bringing to public attention” a criminal method, claiming it will “give villains ideas they never would have had”.

“Whilst Prof Jamieson may be right to have concerns about the planting of false trails by criminals, designed to implicate others as suspects, I don’t think he should broadcast ways for villains to confuse cases against them,” said the forensic scientist.

“Many offenders are not very bright and wouldn’t have thought of this angle. He is giving them ammunition.”

Kathryn Mashiter, scientific support manager for Lancashire Constabulary, said that although planting DNA evidence at a crime scene may pose a risk to investigations, it is difficult to do in reality.

“If criminals are aware of super-sensitive DNA detection methods, it would be fair to say that leaving incriminating evidence at a crime scene is something investigating officers should be aware of.

“Also,” she added, “scenes of crime officers are fully aware of issues related to secondary