The circumstances surrounding the murder of an RUC officer 27 years ago are to be investigated, Northern Ireland Police Ombudsman Mrs Nuala O'Loan said last night.
Sgt Joe Campbell (59), a Catholic, was shot as he locked up his small station in the seaside village of Cushendall on the Antrim coast.
A police colleague was later acquitted of his killing, one of the most mysterious in the history of the violence in the North.
Mrs O'Loan has called in her own officers to make inquiries after claims by Sgt Campbell's family of security force collusion with loyalist paramilitaries.
The ombudsman said: "Based on those inquiries, we feel that there are certain aspects of events before and after Sgt Campbell's murder which demand investigation."
In the 1990s the Campbell family called for an independent inquiry into the killing. Mrs O'Loan stressed that her officers would not be re-investigating the murder itself. "There has been a lot of speculation about police involvement in the murder and this has caused a great deal of distress and anxiety to the Campbell family over the years.
"The speculation has been damaging to both the family and policing in Northern Ireland, and it is in the interests of both that we do all we can to discover the truth about whether or not police misconduct played a part in this murder."
She warned Mr Campbell's family, his former colleagues and the people of Cushendall that the investigation would not be easy.
"This will be a very difficult investigation as no doubt some of the people we may wish to speak to are now dead.
"We are also fully aware that information and memories from more than 25 years ago may not be complete," she added.
The mystery surrounding Sgt Campbell's murder has led to speculation that members of the security forces were involved.
A detective sergeant in RUC Special Branch who was charged with his murder was later acquitted after a trial in 1982.
The detective sergeant had faced a total of 27 charges including having explosives and firearms and carrying out armed robberies in north Antrim.
He was sentenced to 20 years after being found guilty of one armed robbery, possession of a rifle and two hijackings, but was acquitted of the murder and other charges.