Gordon Brown was joined on the campaign trail today by the mother of murdered model Sally Anne Bowman as he sought to portray the Tories as soft on crime.
The Prime Minister attacked Conservative plans to remove innocent people from the DNA database, saying the move would make it more difficult for the police to fight crime.
He was joined for a visit in Stevenage, Hertfordshire - a marginal seat which Labour needs to defend from the Tories - by DNA database campaigner Linda Bowman.
Her daughter's murderer, Mark Dixie, was only caught because he was picked up in a pub brawl.
Even though he was not convicted, his DNA was taken and connected to Sally Anne's murder.
Mr Brown said: "Linda Bowman is a remarkable and brave woman who has suffered the most unspeakable tragedy yet still manages to be a compassionate campaigner for good.
"As Mrs Bowman says, the use of DNA helps the police put the most dangerous criminals behind bars but can also exonerate the innocent."
Labour promises to keep the DNA profiles of those who are arrested but not convicted for six years.
The Tories want to remove the profiles of people who are not convicted.
Home Secretary Alan Johnson, who also joined the Prime Minister, added: "The Tories might try to talk tough on crime but their actions are weak.
"Their plans for DNA would make it much harder for the police to catch criminals, putting the public at greater risk."
Stevenage is number 72 on the Tories' target list of constituencies for the General Election.
It was taken from the Conservatives by Labour in the 1997 landslide, but retiring MP Barbara Follett's majority was slashed to just 3,139 in 2005.
Mr Brown, joined again for campaigning by his wife Sarah, was shown around a small shopping precinct by Labour's candidate for Stevenage, Sharon Taylor.
They visited the area's Mentoring Basketball Association, project to get young people off the streets in an area which has had problems with anti-social behaviour.
Mr Brown then met local people grouped around a series of tables at the Oval Community Centre.
Speaking at the community centre, Mr Brown restated Labour's commitment to neighbourhood policing and the use of CCTV.
He paid a "special tribute" to Mrs Bowman, who was there, for her "courage and bravery" and for campaigning on keeping the DNA profiles of people who are arrested.
"Because we have insisted on DNA being retained we have been able to find guilty and bring to justice thousands of people guilty of violent crimes, including murder and rape, who would otherwise not be brought to justice," the Prime Minister said.
He added: "I am sorry to say that the Conservative Party has turned its back on its traditions and now want to destroy that data that would help us in the fight against crime."
Shami Chakrabarti, director of campaign group Liberty, said: "Election fever seems to be confusing the debate about DNA retention.
"It has been suggested that the tragic case of Sally Anne Bowman was only solved because her murderer was 'an innocent' on the database.
"In fact, he was arrested for a separate violent offence and it was then that his DNA was matched to the crime scene.
"We all agree that DNA taken on arrest should be checked against unsolved crimes - this is entirely different from stockpiling the DNA of innocent men, women and children for years on end."