More than 100 suspected rapists behind attacks in London going back more than two decades remain unidentified, despite detectives and forensic scientists discovering their full DNA profiles during a trawl of unsolved cases.
The profiles were uncovered during a re-examination of crime archives from the 1980s and 1990s using techniques not available at the time. One of the suspected attackers is believed to be responsible for at least two rapes.
Their identities remain unknown as there is no match on the national DNA database which contains more than five million samples from crime scenes or individuals arrested or detained by police since 1995. Detectives said the suspects are only likely to be caught if they are detained for a new offence and the link is discovered after a DNA swab is taken. They cited the case of Tabir Ali, a serial sex attacker who subjected a mother to a horrific ordeal at knifepoint. He was finally jailed 16 years after the attack when a DNA match was found after he was involved in a domestic incident in 2007.
"It's potentially 100 guys sitting at home that one day could get a knock on the door," said Detective Inspector John Foulkes of the Metropolitan Police's rape review team. "But it may be that they are dead or spent a very short time in the country and left."
His unit has examined some 4,500 unsolved sex attacks covering 1988-90 over the last five years. The small team of eight detectives has already secured five convictions this year. It has now started to re-examine cases from 1991.
Its latest success saw the so-called M25 rapist, Antoni Imiela, found guilty last week of raping a woman on Christmas Day in 1987.
Although samples were retrieved at the time, a DNA profile was obtained only in 2009 when the were retested. Imiela, who was told that he was likely to spend the rest of his life behind bars, had already served eight years in prison for the rapes of seven women and girls between 2001 and 2002 and had been eligible for parole.
The cases have highlighted the technological advances which has seen DNA obtained from ever smaller amounts of potential material kept in the freezers of the state-run Forensic Science Service (FSS) – which is being closed on financial grounds – and in police storerooms. The archive has been reprieved so inquiry teams can investigate historic cases.
Detectives working for the rape investigation team, based in west London, have gone back through files to identify whether there is potential material that can be re-tested.
"It's a kind of weeding process... it's whittling them down to cases which are suitable to look at forensically," said Det Sgt Mick McInerney.
If a match is found, detectives attempt to build the case and find the victims. In most cases, the women agree to help police pursue their case.
"Every single case brings some closure," said DI Foulkes.