Police have arrested a sixth person in relation to the death of Constable Ronan Kerr.
A women, 23, was arrested in Omagh today.
Police continue to question five men in relation to the murder of a Catholic police officer.
Constable Ronan Kerr, 25, was killed by a car bomb outside his home in Beragh, Omagh, on April 2. After a major security operation, which saw raids across three counties, involving 200 officers, police arrested five men yesterday, in relation to the incident.
The investigation is being led by the Serious Crime Branch, who arrested the men, aged 22 to 46, under the Terrorism Act, before taking them to Antrim police station for questioning.
Dissident republicans have been blamed for the murder. Police have already charged one man from Omagh.
Detective Superintendent Raymond Murray, the officer in charge of the investigation, said: ''Our determination to pursue every possible line of inquiry remains undiminished.
Police seized clothing, mobile phones, computers and cars during the raid, which will undergo forensic analysis.
Searches were carried across five counties; Coalisland, Co Tyrone, Toome, Co Antrim, Bellaghy, Ballyronan and South Derry.
Det. Sup. Murray added: ''The investigation is progressing and police have been encouraged by the support and assistance which has been forthcoming from across the community.
''During this search stage, we would ask for people's continued patience and co-operation as we work to complete our inquiries to maximum effect, as expeditiously as possible and with the minimum amount of disruption to community life.''
Constable Kerr joined the police in May 2010, after the Royal Ulster Constabulary became the PSNI in 2001. His murder is the second since the change.
Police have offered a £50,000 reward for information leading to the arrest and conviction of those responsible for Constable Kerr's death.