A man accused of stabbing PC Keith Blakelock during the 1985 Tottenham riots has been found not guilty of murder.
Nicky Jacobs, who was 16 at the time of the attack, had maintained his innocence throughout.
There were cheers from the public gallery as the verdicts were returned by a jury, who took just six hours to clear the 45-year-old with a majority of 10-2.
PC Blakelock was killed by a mob armed with knives and machetes at the height of the riots at the Broadwater Farm estate in 1985.
Estates were devastated during the riots
The 40-year-old was among a group of officers sent out without cover on the night of Sunday, October 6 to protect firemen tackling fires.
He suffered 43 wounds and was left with a knife embedded in his neck.
Mr Jacobs stood and punched the air as he was cleared, before breaking down in tears.
Those supporting him in the public gallery included Winston Silcott, whose conviction for the murder of PC Blakelock was quashed in 1991.
Mr Silcott shouted "Yeah, yeah" and "Brother, brother" from the gallery. Once outside he told reporters: "The police are bitter about what happened, that's why they brought this case.
"Vengeance, that's what the police were out to get."
Winston Silcott at the Old Bailey
PC Blakelock's family, who were in court, have said they are "extremely sad and disappointed at the verdict".
Police have justified pursuing Mr Jacobs almost three decades after the riots in north London and pledged to continue to seek justice for PC Blakelock's death.
Assistant Commissioner Mark Rowley said: "No matter how difficult an investigation it has been to carry out - given the many years that have passed, the lack of forensic evidence and CCTV, plus the main witnesses to Keith murder's being those taking part in the riot - it was important we exhausted every possible lead we could.
"Sadly, Keith's widow, family and friends still have not seen anyone brought to justice for his murder. The dignity, extraordinary patience and courage they have shown in their nearly 30-year quest for justice is humbling.
"We will not give up on bringing Keith's killers to justice.
"There are people who know exactly who took part in the attack on Keith and people who took part themselves. It is not too late for you to come forward. Almost 30 years on, people's lives are very different, their allegiances broken or shifted. Help us now."
PC Keith Blakelock's widow, Elizabeth Johnson
The Crown Prosecution Service also insisted "it was right" to bring a case because "there was sufficient evidence for a realistic prospect of conviction and it was in the public interest".
The trial heard from three anonymous witnesses who claimed to have seen Mr Jacobs take part in the killing.
During investigations into the attack on PC Blakelock a decision was made to give immunity to so-called "kickers" - those who were involved in the attack but did not use weapons.
In exchange they would cooperate with prosecutions, and the jury was told that some witnesses received payments.
Detective Superintendent John Sweeney, who led the investigation for 14 years, insisted: "No-one has been rewarded for this trial."
Mr Jacobs had previously been convicted of affray in 1986 and was photographed at the scene throwing petrol bombs at the police.
Police made numerous arrests at the time
The defendant had written a rap poem during his time in a juvenile detention centre in which he boasted about "chopping" at the officer.
Defending, Courtenay Griffiths QC said: "Bob Marley wrote I Shot The Sheriff but I have not heard of him being put on trial for murder."
The riots on Broadwater Farm are among the worst civil disturbances ever seen in Britain.
Violence erupted on October 5, 1985 after Cynthia Jarrett died of a heart attack following a police search of her home in Tottenham.
This came a week after police shot a black woman in Brixton.
Mr Jacobs was the seventh person to be tried for the Blakelock killing.
Three men, including Mr Silcott, were convicted in 1987 but later cleared on appeal after allegations of fabricated evidence. Three juveniles were acquitted before their case reached a jury.
Stafford Scott, from the Tottenham Rights Group, said the police should now close the case.
Stafford Scott from the Tottenham Rights Group
"This time around we've been given justice. We hope this puts an end to the case," Mr Scott said outside court.
"We feel sorry for the family of PC Blakelock but they shouldn't have been drawn through this because this case should never have happened.
"They've investigated this for 10 years and we've seen a jury release Nicky Jacobs in less than seven hours.
"I think for the police this really is the end of the route."
Mr Jacobs will be released from Belmarsh prison on Thursday.