The trial opened on Monday over the infamous murder of British policeman Keith Blakelock during 1985 riots in London, with prosecutors describing how an armed mob attacked him shouting "kill the pig".
Blakelock, who was stabbed more than 40 times, was almost decapitated during the frenzied attack on the Broadwater Farm housing estate in Tottenham, the Old Bailey court heard.
Nicholas Jacobs, 45, is accused of being part of the mob that set upon Blakelock as he tried to protect firefighters tackling a blaze during the riots. The defendant, who was 16 at the time, denies murder.
He was charged last year with attacking Blakelock with a bladed weapon following an extensive police re-investigation into the murder.
Opening the prosecution case, lawyer Richard Whittam described the policeman's final moments, saying: "The attack on him was without mercy. In the ferocious attack his helmet came off.
"He was beaten and stabbed to death before his colleagues were able to force the attackers away.
"PC Blakelock suffered something in excess of 40 stab-type injuries and there appears to have been an attempt made to decapitate him."
Three people had previously been convicted of Blakelock's murder, but their convictions were quashed by the Court of Appeal in 1991, the court heard.
In a bid to secure a prosecution, some members of the mob who were not armed were given conditional immunity so they would testify against Jacobs, the jury was told.
The rioting erupted the day after Cynthia Jarrett, a mother of a suspect arrested by police, had a heart attack and died when officers searched her home in Tottenham -- the same north London suburb where riots broke out in 2011.
The court heard that the riots in 1985 were "more sinister" than the unrest 26 years later.
Jarrett's death fuelled existing tension between the local predominantly Afro-Caribbean community and the police. When trouble began on October 6, 1985, at least some of the rioters "appeared to have as their target the death of a police officer", Whittam told the jury.
Blakelock was among a group of officers sent to protect firefighters. When they arrived, they came across a "very large group" of rioters, many of them armed, the lawyer said.
Outnumbered, the firefighters and police retreated but Blakelock and another officer, Richard Coombes, were caught.
"Outside the flats, as they ran for safety, PC Blakelock and PC Richard Coombes went to ground and were set upon to shouts of 'kill the pig' and the like," Whittam told the court.
"PC Coombes was very fortunate to survive. PC Blakelock did not."