A 35-year-old woman has been released by police investigating a dissident republican bomb attack on a prison officer in Belfast.
The suspect was detained in the city on Thursday, according to a Police Service of Northern Ireland spokesman.
Officers have been granted an extra 24 hours to continue to question three men, aged 34, 39 and 45, who were arrested on Sunday evening.
The prison officer, a 52-year-old married father-of-three, needed surgery after an explosive device detonated under the van he was driving on Friday March 4.
It is understood he is now out of hospital.
A group calling itself the New IRA claimed to have carried out the attack.