A former RUC detective who was questioned by officers from the Police Ombudsman's office has been released without charge.
Mr McCord was beaten and his body was left at a quarry
Johnston Brown was arrested at Belfast International Airport on Wednesday.
The arrest was part of an inquiry by the ombudsman into the RUC's investigation of the UVF murder of Raymond McCord Junior in 1997.
He 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 without charge.
One of the officers arrested was former CID detective Trevor McIlwrath.
Police Ombudsman investigators questioned them over allegations of perverting the course of justice and misconduct in public office.
Two premises were also searched by the investigators, the Police Ombudsman's office said.
Mr McCord, 22, was beaten to death by members of the UVF and his body left at a quarry in Newownabbey.
Sharon McKenna was murdered in north Belfast in 1992
It has been claimed that at least one of those responsible for the McCord murder was working for police Special Branch at the time and this led to a major investigation by Police Ombudsman Nuala O'Loan.
It is understood the investigation, which has been going on for several years, has mushroomed into a wider inquiry involving police intelligence-gathering methods and the use of informers.
The ombudsman's investigation also includes the UVF murder of Sharon McKenna in north Belfast in 1992.
The 27-year-old Newtownabbey taxi driver was shot in the sectarian attack at the home of an elderly friend whose dinner she was making.
An interim report has already been submitted to the Public Prosecution Service and a report is expected to be published next month.