The Metropolitan Police confirmed yesterday it was conducting a major "cold case" review of the existing evidence in a fresh attempt to identify his murderers. It said it had received no new information.
Pc Blakelock was hacked to death with a machete during the 1985 Broadwater Farm riots in Tottenham, north London, a killing which marked a previously unseen level of violence towards the police.
Now detectives are DNA-testing clothes which were removed from six men arrested at the scene and regarded as suspects.
Advances in forensic science mean that even evidence such as skin particles, invisible to the naked eye, can be identified and tested. Blood samples can also be examined to find out if they came from Pc Blakelock and whether the spattering pattern indicates that any of the suspects could have carried out the killing.
The move comes after the Metropolitan Police last month agreed to pay Winston Silcott, who was convicted and then cleared of the killing, a pounds 50,000 out-of-court settlement for alleged malicious arrest and false imprisonment.
Relatives of Pc Blakelock, including his widow and three sons, expressed outrage at the award to Silcott, who is currently serving a life sentence for a separate murder.
Senior officers have justified the settlement, pointing to the high cost of defending the case, and legal advice they received.
Officers are also asking for up to 50 others who were not involved in the killing, but who were at the scene and may have been witnesses, to come forward with information.
A spokesman for the Police Federation said he was confident the new inquiry would lead to a conviction.
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