Eyewitness 'John Brown', a former member of the Park Lane Boys gang, who accepted a caution for assaulting his partner in 2010, said defendant Nicky Jacobs used a machete with a 12-inch blade during the attack on Pc Keith Blakelock.
He told the jury that he himself had kicked the officer some 10 times after he went to the ground.
Asked why, he said: "Looking back on it I don't know...It was the excitement of the situation, I just rushed forward and kicked him about ten times."
The witness said he had been paid a £5,000 reward by the police after giving a statement during a renewed police investigation into the killing in 1993.
PC Blakelock curled up in a ball and screamed for help as a mob hacked him to death during the Broadwater Farm riots, an eyewitness has told the Old Bailey.
Using the pseudonym John Brown and with his voice distorted by a modulator to protect his identity, the witness described how he saw the killing on the estate in Tottenham, north London, on October 6 1985.
He explained that he had seen Nicky Jacobs, 45, stabbing PC Blakelock with a machete between two and four times as the frenzied mob took part in a "free for all".
Asked by Richard Whittam QC, for the prosecution, what the officer was doing during the attack, Mr Brown said: "What I saw, he was trying to curl up into a ball, I suppose to protect himself somehow.
"Did he say anything?" Mr Whittam asked.
"I just heard heard screams of 'help, help, help'."
The sergeant in charge of Pc Keith Blakelock's unit has described the "absolutely terrifying" moment they came under attack by a mob armed with iron bars and a machete.
David Pengelly led his team of 10 officers to protect firefighters tackling a blaze at the Broadwater Farm estate.
When they arrived, he said: "There were lines of officers with shields. There were missiles being thrown. It was a scene of considerable rioting."
As the team went with firefighters to the blaze, it was Pc Blakelock who suggested someone should stay by the stairwell to protect their exit, which he and another officer then did.
Mr Pengelly said: "I saw a group of youths. My eye was drawn to youths who were running underneath us. A group appeared at the far side of the level we were on from an entrance of some sort."
One rioter he noticed had muslin covering his face, with eye holes cut into it, he said.
Mr Pengelly raised his visor to shout at the crowd that they were just there to "protect the firemen".
He went on: "There was something perhaps of a dramatic pause. I do not know the reason. Then another group appeared slightly to the right from an unknown point to me.
"There was no time to reflect as the second group immediately starting throwing items at us - bottles, bricks, I believe mainly."
Some of the youths then started to run around to "effectively out flank us and cut off our retreat" so Mr Pengelly gave the order to retreat down the stairs to the ground level.
"Obviously at this point, the rioters were right with us hammering on the shields. It was an absolutely terrifying scenario.
"As we retreated down the stairway there were people with iron bars and at least one with a machete, effectively trying to chop the shields to bits. The retreat to ground level was just a continuing nightmare."
It's alleged the suspect in the PC Blakelock murder wrote a rap about the killing while serving a sentence for affray. Nicholas Jacobs is alleged to have written:
"Me have de chopper we have intention to kill an police officer PC Blakelock..."
The rap went on "he beg for mercy but it didn't matter.. him get capture. Him have to face consequences."
A police officer was stabbed to death during the 1985 Broadwater Farm riots after he was set upon by an armed mob yelling "kill the pig", a court heard.
Nicholas Jacobs, 45, is accused of murdering Pc Keith Blakelock, 40, as the officer tried to protect firefighters tackling a blaze at the height of the unrest in Tottenham, north London.
The Tottenham riots of 1985 erupted the day after Cynthia Jarrett, a mother of a police suspect, had a heart attack and died when her home was searched in Thorpe Road, Tottenham.
Pc Blakelock was among a group of uniformed officers sent out without cover on the night of Sunday October 6 1985 to protect firemen putting out blazes.
They came across a "very large group" of rioters, many armed with an assortment of weapons, the court heard.
"Very heavily outnumbered and fearful they may become trapped both the police and the firefighters were forced to retreat. 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.
"Pc Coombes was very fortunate to survive. Pc Blakelock did not. 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."
Jacobs denies the murder. The trial continues.
The trial into the murder of PC Blakelock during the Broadwater Farm riots in 1985 is underway.
The prosecution claims the defendant was armed with a knife and was part of a group of 15-20 people in the inner circle of those attacking PC Blakelock. It's also outlined the two previous investigations into his murder.
The trial of the man charged with the murder of PC Keith Blakelock during the Broadwater Farm riots in 1985 is about to begin at Old Bailey. The man charged, Nicholas Conrad Jacobs, denies a single count of murder.
The jury is made up of 7 men and 5 women. It is alleged that the defendant was armed with a knife and was part of the group that attacked PC Blakelock.
A very visible, vocal group outside the Old Bailey on behalf of Nicholas Jacobs. He denies murdering PC Keith Blakelock in the Broadwater Farm riots of 1985. The trial starts this morning.