Two former RUC detectives arrested yesterday in connection with investigation into the loyalist murder of Raymond McCord jnr in 1997 have been released without charge.
A third former detective, Johnston "Jonty" Brown, was also arrested last evening by Police Ombudsman Nuala O'Loan's investigators at Belfast International Airport after returning from a holiday abroad.
Mr Brown was detained in connection a major inquiry into suspected police collusion with loyalist paramilitary killers in Northern Ireland.
Ombudsman Nuala O'Loan, who is carrying out a major investigation into the case.
The retired sergeant had previously been interviewed voluntarily by Mrs O'Loan's team since he left the force in 2001 and began revealing highly embarrassing and damaging details of police Special Branch work with paramilitary informers.
He was heavily involved in the police undercover operation that led to the 1994 arrest and conviction of feared loyalist commander Johnny "Mad Dog" Adair.
Before his return to Northern Ireland, his home in Ballymena was searched, and computer equipment and other items were taken away.
The first two ex-CID men detained, Chief Superintendent Tom Meek and Constable Trevor McIlrath, were later released without charge.
Mrs O'Loan's inquiry was originally centred on the RUC's handling of an investigation
into the death of former RAF man Raymond McCord Jr, who was beaten to death by the Ulster Volunteer Force (UVF).
The inquiry has now widened to include the 1993 shotgun murder of a Catholic woman taxi driver in north Belfast.
Ms Sharon McKenna (27) was killed by two UVF men who opened fire with a 12-bore shotgun as she cooked dinner for an elderly friend at his north Belfast home in January 1993. She was shot a second time as she lay dying on the floor.
The investigation into the murder of Mr McCord (22), whose body was dumped in a quarry just outside Belfast in 1997, is the biggest ever undertaken by Mrs O'Loan and her team.
They have already prepared a damning report which is expected to include claims that loyalist paramilitaries working as police informers at that time were involved in a series of killings but were never charged.
A file on the alleged scandal has been submitted to the Public Prosecution Service, and the report is expected to be published next month.
At least one of those responsible for Mr McCord's murder worked for Special Branch, it has been claimed.