Damning documentary evidence has conclusively shown that the RUC learned the truth about informer Mark Haddock years before he was toppled as a paramilitary godfather.
A previously confidential letter has proved that detailed allegations on Haddock's killing spree were spelt out to police headquarters in 2000.
That was three years before a major investigation by Ombudsman Nuala O'Loan finally brought an end to the UVF man's double life as a paid Special Informer.
During that period, his north Belfast murder gang continued to build its crime and drugs empire, committing murder and other acts of terrorist violence.
The existence of the letter was revealed by this newspaper last month but its contents have remained unknown - until today.
The letter raises fresh questions over the RUC's handling of the Haddock case. It also creates further problems for the PSNI as it faces legal action from families of the informer's victims.
It was written by campaigning father Raymond McCord and sent to the Stevens collusion inquiry team.
It was forwarded to the office of Chief Constable Sir Ronnie Flanagan at RUC headquarters in September 2000.
He is understood to be adamant that he did not see the letter, which raises questions about the RUC's handling of such sensitive correspondence.
Mr McCord last night said: "I did not keep a copy. I was confident that I had spelt out chapter and verse about Haddock but could not prove this without the letter. Now the PSNI have released a copy to me and it vindicates everything I have been saying.
"People cannot say the RUC was unaware of the allegations. They are there in black and white."
In the letter, Mr McCord named Haddock as a Special Branch informer and leader of the Mount Vernon UVF.
He said the 1997 murder of his son, Raymond jnr, was carried out on Haddock's orders - a claim backed up in the report published last month by Police Ombudsman Nuala O'Loan.
He also stated that the Mount Vernon UVF had carried out other killings including that of Catholic woman Sharon McKenna in 1993 and Protestant Billy Harbinson four years later.
"Not one person has been charged with any of these murders even though the UVF in this area is full of informers," Mr McCord's letter stated.
It also said: "RUC men have told me privately that every investigation concerning Haddock hits a brick wall, i.e. someone puts that brick wall there."
In a plea to the Stevens inquiry team, Mr McCord added: "Is it right that a 'man' can work for the security forces and also be granted immunity or else be allowed to murder due to his handler protecting him? My family and me hope and pray outside people like yourself will expose what is going in our country and see that justice does exist."
The PSNI's present chief constable Sir Hugh Orde worked for the Stevens team in 2000. He told the Belfast Telegraph last month that Mr McCord's letter was forwarded to Sir Ronnie Flanagan in September 2000, as it was outside the remit of the Stevens investigators.
The PSNI subsequently said the document was dealt with by the force's command secretariat - the chief constable's office. It stated that the letter was sent to the officer investigating the Raymond McCord jnr murder case.
Sir Ronnie has been contacted by this newspaper about the September 2000 letter, but has not commented. He is now head of Her Majesty's Inspector of Constabulary, which oversees all UK police forces.
He is understood to be privately emphatic that he did not at any time see the correspondence forwarded by the Stevens team.
This would mean that he did not personally deal with a matter raised by a high-level outside police team conducting a major collusion investigation.
In a statement last month, Sir Ronnie stated: "With respect to the specific matters dealt with in the Ombudsman's report, at no time did I have any knowledge, or evidence, of officers at any level behaving in the ways that have been described."
Mrs O'Loan's report stated that Haddock was not struck off as a police Special Branch informer until 2003, when Mrs O'Loan's office alerted Sir Hugh to the facts it was uncovering.
Haddock was paid an estimated £80,000 during his 12 years of informing.
The O'Loan report linked him and his UVF associates to at least 10 killings. These included the murder of loyalist politician Tommy English in October 2000 - one month after the Stevens team contacted the RUC about the McCord allegations.
In December 2002, Haddock led a gang in a knife and hatchet attack on Ballyclare man Trevor Gowdy. He is currently serving a jail sentence for this vicious assault - also committed while he was still an informer.
Mrs O'Loan's report stated that Special Branch's shielding of Haddock had " consolidated and strengthened" the UVF's position in north Belfast.
The Ombudsman also said that he would have been "well aware of the level of protection which he was afforded".
Relatives of four victims of the Mount Vernon UVF are suing the PSNI in the wake of the Haddock revelations.