The widow of Pc Keith Blakelock wept after a man accused of stabbing her husband to death during the Tottenham riots nearly 30 years ago was found not guilty.
Pc Blakelock was attacked by an armed mob after his unit was deployed to protect firefighters tackling a blaze on the Broadwater Farm estate in north London on the night of October 6 1985.
The Old Bailey trial heard that the 40-year-old beat bobby was stabbed more than 40 times and rioters tried to decapitate him, leaving a knife lodged in his head.
Nicky Jacobs, who was 16 at the time, was the seventh person to be charged with the officer's murder b ut no-one has been brought to justice for the killing.
When the not guilty verdict was delivered, Pc Blakelock's widow, Elizabeth Johnson, left the courtroom and wept, while her three sons held their heads in their hands.
The family later issued a statement saying they were "extremely sad and disappointed".
Meanwhile, Jacobs punched the air and sobbed in the dock as supporters in the public gallery gave out shouts of joy.
Jacobs supporter Stafford Scott said afterwards that questions should be raised with the Crown Prosecution Service and Director of Public Prosecutions as to why such a "farcical" case came to trial.
He told reporters outside the court: "It is not a day of joy. Everybody should be able to take the notion of receiving justice as standard."
But the Crown Prosecution Service said that, while it accepted the verdict, "it was right" to bring the case against Jacobs.
And Scotland Yard Assistant Commissioner Mark Rowley vowed: "We will not give up on bringing Keith's killers to justice."
He said: "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."
Jacobs' prosecution followed an earlier trial in 1987, when three men were convicted of the murder but later freed on appeal. The case against three youths was dropped.
During the course of three separate investigations, a controversial decision was made to give immunity to so-called "kickers" - those who were involved in the attack but did not use weapons - in exchange for their co-operation.
Among them were the prosecution witnesses given the pseudonyms Rhodes Levin and John Brown, who both admitted kicking Pc Blakelock and were given amnesty from prosecution.
Some of the witnesses also received payments from police for their co-operation, the jury was told.
Jacobs' lawyer, Courtenay Griffiths QC, dismissed their evidence as "bereft of coherence, riddled with lies, incoherent and contradictory".
Other evidence presented to the court included a rap poem about the murder which Jacobs wrote while in custody.
The poem read: ''Me have de chopper we have intention to kill an police officer Pc Blakelock de unlucky f***er him dis an help de fireman."
Of this evidence, Mr Griffiths said: "Bob Marley wrote I Shot The Sheriff but I have not heard of him being put on trial for murder."
The Old Bailey trial also heard that in May 2000 Jacobs was arrested and told a police officer: "F*** off, I was one of them who killed Keith Blakelock."
The riots erupted the day after a suspect's mother, Cynthia Jarrett, had a heart attack and died during a police search of her Tottenham home.
It followed weeks of tension and concerns that ''individuals were planning public disturbances'' in the borough of Haringey.
Prosecutor Richard Whittam QC said the riots were more ''sinister'' than the later ones in 2011, and at least some rioters were intent on killing a police officer.
Pc Blakelock was among a group of uniformed officers who came across a ''very large group'' of rioters, many armed with an assortment of weapons, the court heard.
He and Pc Richard Coombes were set upon by a crowd of rioters shouting "Kill the pig", the court heard.
The attack on Pc Blakelock was "without mercy", his helmet came off and there was an attempt to decapitate him, jurors were told. Pc Coombes survived.
Jacobs is now expected to be released from Belmarsh jail, but the Prison Service refused to confirm whether it would be today.
Mr Scott said Jacobs is not expected to be released until tomorrow morning as the administrative offices at Belmarsh have closed.