Two men have been arrested by detectives investigating alleged criminal activity within the Northern Ireland Police Ombudsman's office.
The men, aged 62 and 67, were detained in England and brought to Northern Ireland for questioning on suspicion of perverting the course of justice and misconduct in a public office.
Their arrests were linked to an investigation by the Police Ombudsman's office into alleged police misconduct in the so-called "Derry Four" case.
The case relates to four teenagers who in 1979 were charged with the IRA murder of British solider Steven Kirby in Londonderry.
The quartet skipped bail and fled across the Irish border. They stayed there for two decades before the charges against them were dropped in 1998.
One of the men subsequently complained to the Police Ombudsman about his treatment by the Royal Ulster Constabulary (RUC).
Following an investigation by the watchdog two former RUC officers were charged with perverting the course of justice.
However, their prosecution collapsed after information that undermined the prosecution case was presented at a late stage in proceedings by the Ombudsman's office.
The episode prompted the Ombudsman to refer the case to the police to investigate potential wrongdoing by Ombudsman's investigators.
The two suspects arrested on Tuesday have since been reported to Northern Ireland's Public Prosecution Service.
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