Detectives investigating the murder of Northern Ireland police officer, Ronan Kerr, are continuing to question a 22-year-old man.
The man, from Omagh in County Tyrone, was arrested in Milton Keynes, Buckinghamshire, on Monday evening.
Constable Kerr, 25, died when a booby-trap bomb exploded under his car in Omagh on 2 April 2011.
Dissident republican paramilitaries have been blamed for the killing of the newly-recruited Catholic constable.
The arrest was made by officers from the North West Counter Terrorism Unit at the request of PSNI Serious Crime Branch detectives.
Mr Kerr, who was a Catholic and an active member of the GAA (Gaelic Athletic Association), was seen by many as a symbol of Northern Ireland's new police service.
The officer joined the PSNI in May 2010.
A republican splinter group claiming it was made up of former members of the Provisional IRA later claimed responsibility for his murder.
He was the second police officer to have been murdered since the Royal Ulster Constabulary became the PSNI in 2001.