The widow of a policeman murdered by a machete-wielding gang 20 years ago has joined police calls for those shielding the killers to come forward.
Pc Blakelock was murdered during a riot on the Broadwater Farm estate
Thursday marks the anniversary of Pc Keith Blakelock's death during riots in Tottenham, London. Three men were convicted, but later cleared on appeal.
Elizabeth Johnson said not knowing who killed him made life "extremely hard".
Images of Pc Blakelock's blood-stained overalls have been released to try to make witnesses come forward.
Police are certain there are people in the area withholding vital information.
Tape marks on the uniform show the number of wounds that were inflicted on the officer in what one of London's top officers Tarique Ghaffur has described as a brutal murder.
Det Supt John Sweeney, who is leading the latest inquiry into the murder, believes the passage of two decades means circumstances may have changed for witnesses who did not come forward at the time.
"I strongly believe that there are people out there with information that could prove vital to our enquiry but who have not yet come forward," he said.
Tape on Pc Blakelock's overalls show where the knife went in
"If they were 15-years-old in 1985 they will be 35-years-old now and could have a completely different outlook on life."
Pc Blakelock, a father of three, was murdered during the riot on the Broadwater Farm estate, sparked by the death of Cynthia Jarrett, 49, who collapsed during a police raid on her home.
Pc Blakelock and his colleague Pc Richard Coombes were attacked when they went on to the estate to protect firefighters as the violence escalated.
Winston Silcott, Mark Braithwaite and Engin Raghip were convicted of the killing in 1987 but cleared on appeal.
In a statement Mrs Johnson, from West Boldon, South Tyneside, said: "For years we have lived with uncertainty of not knowing who is responsible for what happened to Keith and this has been extremely hard to live with.
"Any family who has suffered a tragic loss of loved one will understand the pain and just how hard it has been for us.
"Not knowing the truth about the circumstances that led Keith's murder just makes it all the more difficult for us."
She asked anyone with information, no matter how small, to come forward "and help us as a family find out the truth".