A former RUC detective questioned about a police investigation into a loyalist murder nine years ago was released tlast night night without charge.
Johnston Brown was arrested the previous night at Belfast International Airport by officers from Northern Ireland Police Ombudsman Nuala O'Loan's office examining the RUC's investigation of the murder by the Ulster Volunteer Force (UVF) of Raymond McCord jnr in 1997.
Mr McCord was beaten to death and his body dumped in a quarry by the UVF in Newtownabbey, near Belfast.
The investigation has been sparked by claims that at least one of the people who murdered Mr McCord was working for Special Branch at the time.
It is understood Mr Brown was questioned about a number of matters, including attempting to pervert the course of justice.
Two other former detectives arrested on Wednesday morning were released yesterday without charge after questioning.
Premises were also searched by Police Ombudsman investigators, who are also looking into the murder of taxi driver Sharon McKenna (27)
in north Belfast in 1992. She was shot in the sectarian attack at the home of an elderly friend.
The Ombudsman's team has focused on intelligence-gathering methods used by the RUC and the management of informers.