麻豆传媒

The first criminal conviction based on a new DNA technique which uses relatives鈥� DNA to track a suspect was made in the UK on Monday.

Craig Harman of Frimley, Surrey was convicted of manslaughter and jailed for six years on the basis of 鈥渇amilial DNA searching鈥�, which linked him to the crime scene via a close relative鈥檚 DNA profile.

Harman threw a brick from a bridge over a motorway which crashed through the windscreen of Michael Little鈥檚 lorry in March 2003. As the brick hit his chest, 53-year-old Little suffered a heart attack, though he still managed to steer his vehicle out of harm鈥檚 way before dying.

Police obtained a DNA profile of the assailant from blood on the brick but could not match it to anything on the UK鈥檚 national DNA database because Harman had no criminal convictions. The database holds about 2.5 million profiles of charged criminals and, since 4 April 2004, suspects who are arrested but not charged.

鈥淚t is another tool for police officers,鈥� says Jonathan Whitaker, of the UK鈥檚 Forensic Science Service (FSS), which developed the technique. 鈥淚t鈥檚 really reserved for those cases where you have got a DNA profile and no match on the database. The whole idea is to keep the momentum going and identify the offender before he does anything else. This case illustrates that really, really well.鈥�

鈥淭here is no doubt in my mind that without this groundbreaking technique this crime would have remained undetected,鈥� says Detective Chief Inspector Graham Hill of Surrey police.

Drunken act

The FSS and police used familial searching to uncover a close relative of Harman鈥檚, who had a criminal conviction and was on the DNA database. The relative鈥檚 profile matched the DNA on the brick by 16 out of 20 points. This lead police to Harman, whose DNA gave a perfect match, and he eventually confessed to the drunken act of violence.

Familial searching comprises of two tests, Whitaker, told 麻豆传媒. The first matches parents to children. Standard DNA profiles examine 10 markers in the DNA. Each marker has two sequences 鈥� one inherited from the mother, and one from the father. The database can be trawled to match potential parents which gives the police 鈥渁 manageable list鈥� to investigate.

Potential siblings can also be matched via the database by comparing markers. 鈥淥n average, two people would probably have six or seven DNA markers in common out of 20, simply by chance,鈥� explains Whitaker, but 鈥渨ith over 12 bands in common, you very, very rarely see unrelated people with that degree of similarity鈥�.

The system was only launched for police investigations in September 2003, so data on the probability of a correct match is not yet available.

False matches

Alec Jeffreys at the University of Leicester, who pioneered DNA profiling techniques, told 麻豆传媒 that the high point score in the Harman case 鈥渟uggests quite a high level of matching鈥�.

But he cautions that close relations could show a 10 out of 20 point match or lower 鈥� particularly if their markers are common in the population. 鈥淓ven unrelated people start to show these sorts of matches,鈥� he says. 鈥淚f you are lucky it could give you a very strong lead straight away. If you are unlucky, you could wind up with lots of false matches.鈥�

Jeffreys believes that if familial searching is to be used more in such criminal investigations 鈥渢his would be a compelling argument to increase the number of DNA markers used鈥�.

He says using familial searching to track people who have never been involved with the law raises 鈥減otentially rather thorny鈥� civil liberty issues. For a serious crime such as Harman鈥檚, the benefits are clear, he says, but for lesser crimes the balance between an individual鈥檚 civil rights and the need to identify a perpetrator may be less obvious.

However, Whitaker says the new technique is compliant with the UK鈥檚 Human Rights, Police and Criminal Evidence and Data Protection Acts. It can only be used for serious offences like murder or serious sexual assault with high level police authorisation.