Senior RUC sources have said a man previously involved in Provisional IRA "punishment" squads was responsible for killing a Protestant taxi-driver, Trevor Kell, in north Belfast this month.
The killing on December 5th has not been admitted by any paramilitary organisation. The RUC Chief Constable, Sir Ronnie Flanagan, had said republicans were involved.
Sir Ronnie has refused to specify whether they were dissident or mainstream. He said it was possible the killing was carried out by "renegade" or "freelance" republicans but has declined to give further details.
However, senior RUC sources have told The Irish Times the gunman had previously been involved in Provisional IRA "punishment" squads in north Belfast. They believed he was acting independently of the Provisional IRA and that the killing was not sanctioned by the leadership.
They said the bullets used in the attack on Mr Kell came from a batch previously used in the attempted murder of an RUC officer in north Belfast. Bullets from that batch were also used in the Provisional IRA murder of two RUC officers in Lurgan, Co Armagh, three years ago, according to the RUC.
The Provisional IRA, the "Real IRA" and the Continuity IRA have all strongly denied involvement. Sinn Fein has said it believes loyalists were responsible. However, the RUC sources said they were "100 per cent sure" the gunman had previously been involved in Provisional IRA "punishment" squads and, despite its denials, its leadership knew this individual was responsible.
The sources said he had no connection with any dissident group and his motivation was sectarian. Mr Kell worked for a taxi depot in a loyalist area.
There had been speculation that a controversial Provisional IRA man from Ardoyne had been involved but RUC sources said they had ruled him out.
They believed the gunman acted "in a freelance fashion" and did not seek authorisation. Local republican sources said this was unlikely. There was no history since the ceasefire of unauthorised Provisional IRA at tacks, they said. "There is a lot of speculation in Ardoyne that the IRA was responsible. If they were, it would be very unlikely the attack wasn't sanctioned.
"If somebody just decided to take an IRA gun and use it in a killing, then the IRA would take action against them very, very swiftly."
A man arrested in connection with Mr Kell's killing has since been released. The murder was followed by three separate loyalist gun attacks in which a Catholic workman, Gary Moore, was killed, and another two men were seriously injured.