A 51-year-old man has been arrested by police investigating the IRA killing of Catholic RUC man Michael Ferguson almost 30 years ago.
The 21-year-old, who was from Omagh, was shot twice in the back of the head at Shipquay Street in Derry in January 1993.
A lone gunman approached Mr Ferguson from behind after he and two officers were called to the Richmond shopping centre following a reported theft from a shop.
He was taken to hospital but died from his injuries.
The suspect was arrested in Derry today under the Terrorism Act and taken to Musgrave Police Station in Belfast for questioning.
In May another 51-year-old was also arrested in connection with the murder.
One man has been jailed for 'assisting' in the killing but the gunman has never been caught.
