Mick Steele and Jack Whomes are serving life for the 1995 murders
A "supergrass" murder trial witness was helped by police to sell his story to the media before the case even got to court, the Appeal Court has heard.
Mick Steele, 64, and Jack Whomes, 45, are serving life for the 1995 murders of three gangsters in Rettendon, Essex.
Their lawyers argue the book, TV and film deal struck by key witness Darren Nicholls made his evidence unreliable.
Prosecutors deny claims of a police cover-up and say they will seek a retrial if the convictions are quashed.
Steele, of Great Bentley, Essex, and Whomes, of Brockford, Suffolk, were convicted at the Old Bailey in 1998 of killing Patrick Tate, Anthony Tucker and Craig Rolfe.
Their bodies were found in a Range Rover in a lane in December 1995.
Baroness Kennedy QC, representing Steele, told the Appeal Court on Wednesday that new disclosures about police involvement in Mr Nicholls' media deal threw "a very different light on police conduct in the trial and their alleged collusion in framing these two men".
She said Nicholls, a criminal who was himself under arrest when he "turned Queen's evidence", had stood to gain financially from the conviction of the accused men.
At the time, she said a series of scandals had led to new rules forcing police to cut back on the amount of money they could spend on supergrasses and informants.
This was to remove the incentive for them to give false evidence.
She told the court: "It was in the absence of sufficient financial incentive that Nicholls, with the knowledge of the police, settled on the idea of selling his story.
"He wanted it set in stone before he committed himself to his role as a protected witness."
She said: "We say that the police, unable to supply finance to the witness themselves, facilitated his link with the media - in contemporary parlance, it was outsourcing or a private finance initiative."
Lady Kennedy said Nicholls went on to give a false story to obtain a greatly-reduced sentence for the crime he was himself accused of.
The media deal - which in the end did not make him as much money as he had hoped - was intended to make up for the money he knew he would lose by curtailing his criminal activities, she said.
The court heard a copyright contract began in August 1996, months before committal proceedings, and a publishing deal was signed in the September.
Lady Kennedy said Nicholls had earlier been involved in a "thoroughly dishonest" relationship with an Essex police officer.
Later, literary agent Caroline Dawnay gave evidence about a £20,000 book deal in 1996 to be shared between Nicholls and Mr Thompson.
At the original trial, prosecutors argued the men had been killed in a gangland dispute over drugs.
Steele and Whomes were also convicted, along with Peter Corry, of Clacton, Essex, of conspiracy to import cannabis.
Corry, who was jailed for four-and-a-half years, is also contesting his conviction.
The story of the murders became known as the "Essex Boys case" after it inspired a film starring Sean Bean.
The hearing was adjourned until Thursday.