Detectives investigating the murder of Jim Donegan outside a west Belfast school arrested a man under the Terrorism Act on Thursday.
Mr Donegan, 43, was shot dead as he waited to pick up his 13-year-old son outside St Mary's Grammar School on the Glen Road on December 4 2018.
The murder, which police have previously attributed to the INLA, was witnessed by hundreds of children and their parents.
Police have also said another republican group, Óglaigh na hÉireann, was also involved in the murder.
On Thursday detectives from the PSNI's Major Investigation Team arrested a 42-year-old man.
After being taken to the Musgrave Serious Crime Suite for questioning the man was released unconditionally.