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.
More top news
Police are appealing for witnesses after a crash involving a car and three pedestrians in Islington.
Five rugby league legends were immortalised in bronze today outside Wembley Stadium.
Four people have been bailed after a three-year-old girl was shot in the stomach with an air riffle while she played in a park.