A third person has been arrested in connection with the murder of Police Constable Ronan Kerr in Omagh last weekend. The 33 year old was detained in the town last night.
Meanwhile, detectives investigating the murder have begun re-opening cold case dissident republican attacks.
The PSNI says groups are continuing to target policemen - detectives are understood to have evidence of attempted attacks since Constable Kerr's murder, a week ago today.
Police have been given more time to question two other men, also being held over the car bomb murder.
The 26-year-old and a 40-year-old man can be quizzed for up to another four days.