A 41-year-old man who was arrested on Tuesday was still being held in custody last night in relation to the failed dissident republican attempt to murder a PSNI officer in east Belfast on Sunday.
Two men, aged 34 and 25, who were arrested on Monday were released unconditionally.
The PSNI officer was bringing his wife and two children to lunch when he checked under his vehicle and discoverd the bomb, which police said could have killed the family.
The device was defused by a British army bomb disposal team and police hope forensic testing of what remains of the bomb will assist them in identifying who was responsible for the murder attempt.
Police have been warned to be on high alert against further dissident attacks.
Similar bombs were responsible for killing Constable Ronan Kerr in Omagh in 2011 and injuring Constable Peadar Heffron as he drove to work in Randalstown, Co Antrim, in 2010.
