Image copyright PAcemaker Photos Image caption Lt Steven Kirby of the Royal Welch Fusiliers was shot in February 1979 in Londonderry

Two former investigators for Northern Ireland's policing watchdog have been arrested on suspicion of conspiring to pervert the course of justice.

The arrests are in relation to alleged misconduct within the office of the Police Ombudsman.

The suspects, aged 62 and 67, were detained in England on Tuesday. They were brought to Northern Ireland for questioning.

Police are to send a file to the Public Prosecution Service.

Detectives have been examining the Police Ombudsman's investigation of the RUC's treatment of the so-called 'Derry Four', who as teenagers were charged with the murder of a soldier in 1979.

They fled across the border and remained outside Northern Ireland for almost 20 years until they were acquitted in 1998.

New information

Their treatment by the RUC was investigated by the Police Ombudsman and in 2012, the matter was referred to the Public Prosecution Service (PPS).

In 2014, the prosecution of two former police officers in connection with the interrogations of the 'Derry Four' collapsed after the PPS received new information from the ombudsman.

In the wake of that collapse, the PSNI was called in by the Police Ombudsman to look at how the complaint by the four men was investigated by its office.