Northern Ireland's Police Ombudsman is investigating "possible police misconduct" by members of the Royal Ulster Constabulary before and after the murder of a Catholic colleague.
A spokesman for Ms Nuala O'Loan confirmed that her team of investigators was looking at the circumstances surrounding the murder of Sgt Joseph Campbell outside a police station in the seaside village of Cushendall, co Antrim.
In one of the most controversial murders of the Troubles, Sgt Campbell (49) was shot with a rifle as he locked up the small RUC station in the village on February 25th, 1977.
He was married with eight children.
Sgt Campbell's family and human rights campaigners believe he was a victim of collusion between members of the security forces and the loyalist paramilitary group, the UVF.
They have passed fresh information to Ms O'Loan's office, which oversees the actions of the Police Service of Northern Ireland and its predecessor, the RUC.
A spokesman for Ms O'Loan said: "An RUC officer, who was arrested and charged with his murder, was later acquitted of Mr Campbell's death.
"Earlier this year, Mr Campbell's family made a number of complaints to us and presented us with fresh information which has not previously been investigated.
"We carried out a preliminary investigation. As a result of that fresh information, we are now investigating certain aspects of events before and after the murder which relate to possible police misconduct. We are not, as yet, investigating Sgt Campbell's murder but only the circumstances surrounding it."
Information compiled by the human rights organisation, British Irish Rights Watch, and by the Sunday People newspaper has also been handed over.
A BBC Panorama programme last week claimed that the British army intelligence force research unit attempted to direct loyalist paramilitary targeting during the Troubles through the agent Brian Nelson, but that its work resulted in the deaths of many innocent Catholics.
The programme also alleged that an RUC officer encouraged two gunmen from the Ulster Freedom Fighters to kill the solicitor, Mr Pat Finucane, in his north Belfast home in February 1989.
The murder of Mr Finucane, and allegations of other security force collusion, are currently being investigated by a team headed by the Metropolitan Police Commissioner, Sir John Stevens.
Among those who participated on the Stevens inquiry team was the new PSNI Chief Constable, Mr Hugh Orde.
Last month the British and Irish governments also appointed Judge Peter Cory to investigate the Finucane murder and other controversial killings.
The Ombudsman's spokesman acknowledged that 25 years on from Sergeant Campbell's murder, it was "not going to be an easy investigation".
He added: "Some of the people we would wish to speak to are now dead."