The PSNI will be investigated into how it dealt with information on a "potential threat" to a man who was murdered outside a Belfast school.
Jim Donegan, 43, was shot dead outside St Mary's Grammar School on the Glen Road on 4 December.
The Police Ombudsman's Office (PONI) said it was looking into whether the information received prior to his murder was properly processed.
Mr Donegan's family has been informed.
On Thursday, police investigating Mr Donegan's murder arrested a 63-year-old man in west Belfast.
The PSNI said on Friday morning that he had been released unconditionally.
The attack happened as the victim was waiting to collect his 13-year-old son from school.
An image of what the suspected gunman may look like has been released by the PSNI.
PSNI Det Ch Insp Pete Montgomery appealed to anyone who witnessed the attack to examine the picture and "help put this extremely dangerous individual behind bars".
"If anyone recognises this person or has any information that could assist with the investigation, please contact 101 and ask for the detectives in Seapark investigating Jim Donegan's murder," he said.