Detectives investigating the murder of Northern Ireland police officer, Ronan Kerr, have been carrying out searches in Dromore, County Tyrone.
Two men arrested over Constable Kerr's murder have been released without charge.
A 39-year-old man from the Omagh area was arrested in Tyrone and a 22-year-old man, also from Omagh, was detained in Milton Keynes, Buckinghamshire.
Constable Kerr, 25, died in a booby-trap car bomb in Omagh on 2 April 2011.
Dissident republican paramilitaries have been blamed for killing the newly-recruited Catholic constable.
The arrest in England was made by officers from the North West Counter Terrorism Unit at the request of PSNI (Police Service of Northern Ireland) Serious Crime Branch detectives.
Constable Kerr, who was also 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 admitted responsibility for his murder.
Constable Kerr was the second police officer to have been murdered since the Royal Ulster Constabulary became the PSNI in 2001.