By Dominic Casciani
BBC News home affairs
Limits are being introduced on the time for which the DNA of people who have been arrested but not convicted can be held on an official database.
How important is DNA to the police? Here are some of the key recent stories - and the role of DNA and the database in what happened.
ARRESTED FOR ONE CRIME - LINKED TO ANOTHER
One of the most important recent cases was the murder of Sally Anne Bowman in 2005. A massive police investigation failed to track down the teenager's killer but drew a blank.
However, forensics officers successfully obtained a DNA sample from Ms Bowman which they suspected belonged to the killer. The following year, a pub chef called Mark Dixie was arrested after a fight and swabbed under the standard procedures.
When his sample was converted into a profile, the database alerted officers of a match to the Bowman crime scene. He was jailed for 34 years - and may never have been caught had it not been for the match.
ARRESTED, RELEASED AND THEN CAUGHT FOR UNCONNECTED CRIME
Birmingham man Abdul Azad was arrested for violent disorder in February 2005 and DNA swabbed, but then released without charge. Under the rules of some countries, his sample would be destroyed and his profile deleted from the database.
Later the same year, a woman was subjected to a serious sexual assault by a stranger 25 miles away in Stafford.
Police had no clues to the attacker's identity. However, forensics officers managed to recover a tiny sample of skin from underneath the woman's fingernails. It was profiled and the database flashed up a link to Azad. He was jailed for six years for sexual assault.
The senior officer in the case said at the time: "We would never have caught him had his DNA not already been on the database - he didn't even live locally so we had no intelligence leads either."
Staffordshire Police have declined to provide the BBC with a picture of Azad.
POOR QUALITY SAMPLES - BUT IMPROVING TECHNIQUES
Genetic fingerprinting is an evolving science. In 1995 a woman was raped at Otford Railway Station in Kent. Police recovered a very poor quality sample of DNA from the woman's clothing.
Jason Clark: Convicted 13 years later
Five years later, Jason Clark was arrested for a drugs offence and sampled. The database flashed a possible match with the rape - but officers dropped the investigation because the match was not good enough.
In 2007 officers returned to the case, knowing that advances in DNA profiling technology meant they could get more conclusive evidence from their poor sample.
They succeeded in proving the DNA belonged to Clark and he was jailed for eight and half years in November 2008.
MISCARRIAGE OF JUSTICE
Sean Hodgson, 57, was sentenced to life in prison for the December 1979 killing of 22-year-old gas board worker Teresa De Simone.
Sean Hodgson: Cleared after 30 years
He spent 30 years in prison on the basis of a false confession and a blood sample match he shared with many other men.
Mr Hodgson's lawyer, Julian Young, was key to ending this miscarriage of justice because he tracked down in storage the original police sample of semen recovered from Ms De Simone's body.
Had the database been operational in 1979, the jury at his trial would have known that Mr Hodgson's unique genetic profile did not match the sample recovered from the scene.
TERRORISM: SAMPLES KEPT FROM A SCENE
Counter-terrorism officers involved in the 7 July suicide bombings investigations recovered many samples of DNA from the bomb factory in Leeds.
Some of these matched the bombers - and others did not. In 2007 they charged three Leeds men with helping the attackers. The trial primarily focused on other allegations - but it also included evidence of the trio's DNA found on items in the bomb factory.
The defence were able to show to the jury however that there was nothing to link the men to the actual property - only items that had been taken inside because they knew the men who carried out the attacks.
This case shows how tenuous DNA evidence can be in some cases. As with many other investigations, police will retain the DNA profiles gathered from the bomb factory in case they link them in the future to anyone else.
THE INNOCENT GIRL: UPSET AT TREATMENT
Teenager Kathryn Lay from Essex was arrested after being wrongly named as playing a part in some trouble on a school bus.
Kathryn Lay: Angry over treatment
She was held in a police cell and made to give a mouth swab to provide a DNA sample. Within an hour, officers realised her arrest was a mistake and that she had nothing to do with the trouble.
She was released without charge. Her mother asked Essex Police to destroy the DNA sample - and they refused, citing national policy. Kathryn now says she has lost faith in the police - the irony being that her late father was a serving officer for 20 years.
THE MAN WHO STOOD UP TO BE COUNTED
John Cann was walking along the street, minding his own business, when he saw a violent drunken man assaulting a woman and trying to smash her windscreen. He stepped in at personal risk to pull the man off the woman and restrain him while police were called. The drunk attacked Mr Cann and knocked him down with an enormous punch.
When police arrived, they arrested Mr Cann, despite witnesses protesting that he was a hero. They made him give a DNA sample which was added to the database. Police only agreed to erase the profile after a campaign backed by the man's MP and a national newspaper.