A 23-year-old woman who was arrested at her home in Omagh, Co Tyrone, on Wednesday, by detectives investigating the murder on April 2nd of PSNI constable Ronan Kerr in the town, has been released from custody.
Five men who had also been arrested as part of the same murder investigation were released earlier.
The six were arrested across three counties in Northern Ireland in an operation which involved 200 police officers.
Const Kerr, a Catholic, was killed instantly when a booby-trap bomb exploded under his car outside his home.