A third former detective is being questioned in a major probe into suspected police collusion with loyalist paramilitary killers in the North.
Johnston “Jonty” Brown was arrested by Police Ombudsman Nuala O’Loan’s investigators at Belfast International Airport after returning from a holiday abroad.
Brown was detained in connection with an alleged attempt to pervert the course of justice and misconduct in public office.
The retired sergeant had previously been interviewed voluntarily by Ms 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.
Mr Brown was heavily involved in the police undercover operation that led to the 1994 arrest and conviction of feared loyalist commander Johnny “Mad Dog” Adair.
His arrest was the third yesterday by staff from the ombudsman’s office examining the RUC’s handling of a probe into the death of former RAF man Raymond McCord Jr, who was beaten by the Ulster Volunteer Force.
Their inquiry has now widened to include the 1993 shotgun murder of a female taxi driver in north Belfast.
The first two ex-CID men detained, Chief Superintendent Tom Meek and Constable Trevor McIlrath, were later released without charge.
Before Mr Brown returned to the North, his home in Ballymena, Co Antrim, was searched. Computer equipment and other items were taken away.
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 Ms O’Loan and her team.
They have already prepared a damning report, which is expected to include devastating claims that loyalist paramilitaries working as police informers at the 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.
Ms O’Loan’s Senior Director of Investigations, Justin Felice, confirmed the complexities of the inquiry had led them to examine the Sharon McKenna murder investigation.
Ms McKenna, a 27-year-old Catholic cab driver, 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 blasted a second time as she lay dying on the floor. The alleged Special Branch agent at the centre of the probe carried out the shooting, reliable sources claimed.