By 
DETECTIVES investigating the IRA killing of a police officer from Omagh have arrested a 51-year-old man in Derry.
Michael Ferguson, 21, was murdered in a gun attack in January in 1993 on Shipquay Street in Derry.
Mr Ferguson was killed by a lone gunman as he and another officer responded to a report of theft at the Richmond shopping centre.
The man has been arrested under the Terrorism Act and taken to the Serious Crime Suite at Musgrave Police Station in Belfast for questioning.