Police searches are being carried out in Northern Ireland and north west England in connection with the murder of police officer, Ronan Kerr.
Constable Kerr, 25, died when a booby-trap bomb exploded under his car in Omagh, County Tyrone on 2 April 2011.
Dissident republican paramilitaries have been blamed for the killing.
On Monday, a Police Service of Northern Ireland (PSNI) spokesperson said the searches are taking place in both Omagh and Cumbria.
In a statement, they said: "Detectives from the PSNI's Serious Crime Branch, with assistance from officers in Cumbria Constabulary and the North West Counter Terrorism Unit, are conducting a number of searches in Northern Ireland and north west England.
"The search activity is in connection with the wider investigation into the murder of PSNI Constable Ronan Kerr in April 2011 and linked incidents."
Officers from the three police forces are involved in the operation. In Cumbria, searches are being carried out in the Penrith area.
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.
In the aftermath of his death, his mother, Nuala Kerr, urged Catholics not to be deterred from joining the PSNI.
He was the second officer to have been murdered by paramilitaries since the formation of the police service in 2001.
In March 2009, PSNI Constable Stephen Carroll was shot dead as he answered a distress call in Craigavon, County Armagh.
Dissident republican group, the Continuity IRA, claimed responsibility for the attack on the 48-year-old married officer.