A 64 year old man has been arrested in connection with the murder of an RUC officer in January 1993.
Michael Ferguson from Omagh was shot twice at close range in the back of the head by an IRA gunman in Shipquay Street in Londonderry.
The 21 year old was taken to Altnagelvin Hospital but died from his injuries.
Detectives from the PSNI's Legacy Investigation Branch arrested the 64-year-old man in Derry in connection with the Catholic policeman's murder. He is being held under the Terrorism Act and has been taken to Musgrave Police Station for questioning.