Police paid thousands of pounds and perks for eyewitnesses to the murder Pc Keith Blakelock in the Broadwater Farm riots, a court heard.
Nicky Jacobs, 45, is accused of stabbing Pc Keith Blakelock, 40, as the officer tried to protect firefighters tackling a blaze at the height of the unrest on the estate in Tottenham north London on October 6, 1985.
The jury in his Old Bailey murder trial heard that two of the prosecution's key witnesses were paid around £5,000 each after they claimed Jacobs stabbed the officer.
Both men were also "made aware" of a £100,000 reward offered by now-defunct tabloid News of the World.
The first witness, who has been granted anonymity and was referred to in court as John Brown, testified against Jacobs in 1986.
But he did not claim he had seen the defendant use a knife until he was interviewed during a renewed investigation in 1993
Afterwards he was rewarded for information despite admitting having himself carried a scaffolding pole during the attack.
Another eye-witness who had given evidence, known by the pseudonym Rhodes Levin, had a "history of addiction spanning several years", the court heard.
Defence lawyer Courtenay Griffiths QC asked the officer leading the current investigation into the killing about the witnesses' reliability.
Questioning detective superintendent John Sweeney, he said: "Is it right that Levin went on holiday to Spain, missed his plane back and then sent the Metropolitan Police the bill for him to get back?"
Mr Sweeney agreed that the witness's travel expenses had been paid for.
The barrister also asked if the MOT on Brown's car had been "sorted out" by Scotland Yard on one occasion.
"It depends what you mean by 'sorted out'," Mr Sweeney said.
"Paid," Mr Griffiths said, to which the officer answered: "Yes".
Mr Sweeney was asked if the pair were paid £5,000 each, but said he could not remember the exact figures.
The court heard that when a second investigation into the killing came to a conclusion in 1994, the CPS decided not to prosecute Jacobs.
"All of the evidence you now rely upon was available for as long ago as 2009 and the bulk of it from 1994," Mr Griffiths said.
Mr Sweeney replied that the decision to charge Jacobs in July last year had been taken not by him but by the Crown Prosecution Service.
Earlier in the day, the highest-ranking officer at the scene where Pc Blakelock was killed described Broadwater Farm as "impossible to police".
But chief superintendent Colin Couch blamed the estate's design, which allowed people to go from one end to another without descending from gangways.
Violence broke out there after local woman Cynthia Jarrett died of a heart attack as police searched her house.
Mr Couch said that on the day of the riots he had met members of Mrs Jarrett's family and community leaders.
Tensions had gone from being "nose to nose, but not violent" during the afternoon to a full onslaught at night, when disturbances broke out on the Broadwater estate.
Waiting outside after sending Pc Blakelock's unit and firefighters into a building to deal with a blaze, he later saw two officers running out and then a "silver lump" lying on the ground.
Then, he said, "four or five jumped on him and appeared to stab him".
Asked about criticisms he received afterwards from rank-and-file police officers, Mr Couch said: "They didn't have the decision to make. I did."
The court heard that a new investigation into Pc Blakelock's death had got under way in January 2000 and was codenamed Operation Worlingworth.
In 1991 the convictions of three men charged under the initial investigation were quashed after questions were raised about their police interviews.
A second investigation between 1992 and 1994, which offered immunity from prosecution for those in the mob who had kicked rather than used weapons on Pc Blakelock, did not result in prosecutions.
Two police officers - detective chief superintendent Graham Melvin and detective inspector Maxwell Dingle - were charged and acquitted of perverting the course of justice in July 1994.
Mr Griffiths suggested that the initial investigation into the riots had been "tainted by corruption and dishonesty from the highest level".
He also asked Mr Sweeney about former Met Police commissioner Sir Kenneth Newman's reference in 1983 to "symbolic locations" in London which black youths regarded as their own territory and where there was hostility towards the police.
Queried whether this had applied to Broadwater Farm, Mr Sweeney answered: "It was certainly seen as a location where the police weren't always welcome."
The trial was adjourned to Monday at 10am.