Sepculation has been rife in recent months that a police ombudsman investigation into loyalist murders has found "explosive and damning" evidence linking Mark Haddock to at least a dozen killings.
There are strong suggestions that Nuala O'Loan's report expected to be published within weeks has found that Haddock was involved in the murders while acting as an informer for the RUC Special Branch.
The report, which has been billed as the most extensive since the Omagh bombing investigation, is expected to implicate six Special Branch officers in the cover-up of more than a dozen murders.
It has been claimed that the report has already been passed to the Public Prosecution Service.
It is understood that the publication of the findings has been held back until a related court case is finalised.
Last month former senior RUC officer Johnston Brown publicly claimed that elements within RUC Special Branch had protected Haddock to ensure that he was not exposed as an informant, despite the fact that they knew he was associated with several killings of Protestants and Catholics.
Last October in the Dail Labour leader Pat Rabbitte named the UVF killer and his victims.
It is understood Haddock was also questioned by police about the murder in 1997 of Raymond McCord jnr whose killing is the focus of Mrs O'Loan' investigation.
It has been claimed that the inquiry, which has been running for more than two years, is the biggest conducted by her office.
Sources said the report would be more controversial than the Omagh probe, which exposed huge failings in the RUC inquiry.
It is understood to be one of the most significant cases of collusion ever uncovered during the Troubles.