Allegations that the security forces protected IRA gunmen who were informants and failed to prevent murders are being investigated by the Northern Ireland Police Ombudsman.
At least six cases, dating back to the 1980s and 1990s, are being examined by Nuala O'Loan's office in Belfast. Several are understood to focus on the role of Freddie Scappaticci, former head of the IRA's internal security unit, who has since been exposed as a British army agent.
The cases are being investigated individually but may be rolled together if evidence emerges that they are linked. The ombudsman's last report was an indictment of RUC special branch handling of agents in an Ulster Volunteer Force unit.
It said police failed to prevent up to 15 murders over 12 years.
Earlier this week a former special branch officer was arrested by the ombudsman's investigators, who are investigating the 1984 IRA killing of a magistrate's daughter outside a church in the Malone area of south Belfast. Allegations have been made that that special branch allowed the weapon used to be destroyed to protect its informant within the IRA.
The family of John Dignam has also approached the ombudsman's office and asked for his death to be re-examined. Dignam was one of three IRA volunteers shot dead by the organisation in 1992. The family claims he was killed to protect an informant.
"In some of these [ cases] there are suggestions that people were protected by the police from arrest and prosecution," Mrs O'Loan told BBC Radio yesterday. "On the republican side the allegation was that there was protection of republican criminals and there was in some cases [ protection of] a republican informant."
The allegations involved "police failure to investigate [ and that] police knew the murder was going to happen and did nothing about it", she said. "If what is being alleged transpires to be the truth, that would be collusion."- (Guardian service)