Shankill bomber Sean Kelly was among three men and a woman released on Wednesday night after being questioned by serious crime branch detectives investigating the murder of former IRA member Kevin McGuigan (53).
It is understood Kelly has instructed his lawyer to seek compensation for wrongful arrest and detention.
McGuigan was shot at his home at Comber Court in the Short Strand area of east Belfast last week, in what is suspected to be a feud between republicans.
A 53-year-old man has been charged with possession of a firearm with intent to endanger life and will appear before Lisburn Magistrates Court this morning.
Suspicion for Mr McGuigan’s death has fallen on ex-Provisional IRA members thought to be taking revenge for the May killing of former Belfast IRA commander Gerard “Jock” Davison in the Market district of central Belfast.
Mr McGuigan, a father of nine, was shot at point-blank range in the head and chest in front of his wife Dolores, outside their home.
His killing has sparked political controversy, with unionists questioning whether the IRA is still active, even though the organisation said it was ending its “war” in 2005 and decommissioning its weapons.
Sources in Belfast claimed one of the weapons used to kill Mr McGuigan may have come from a batch of guns smuggled in from Florida by the IRA during the peace process in 1999 to defend itself from attacks by former enemies.
Mr McGuigan’s relatives have used social media to accuse the IRA of involvement. However, Sinn Féin has rejected the suggestion of IRA involvement.
Three people were arrested on Wednesday in connection with the investigation.
A 26-year-old man was arrested in Co Antrim area on Wednesday night, while, a 49-year-old man was arrested in the city in the morning and a 32-year-old woman was arrested in the afternoon.
Four other men - aged 53, 44, 41, and 39 - were arrested on Tuesday, before and after Mr McGuigan’s funeral.
The 53-year-old has been charged, while the men aged 44, 41 and 39, and the woman, have all been “released unconditionally”. The men aged 26 and 49 remain in custody.
Belfast bombing
One of those questioned and then released was Shankill bomber Sean Kelly, who was responsible for the October 1993 bombing at a fishmongers in Belfast that killed nine Protestants and IRA man Thomas Begley.
His victims included a seven-year-old child, a teenage girl and an elderly couple. A total of 57 people were injured, some seriously.
It is understood Mr Kelly, released from prison in 2000 under the terms of the Belfast Agreement, was in Co Donegal at the time of Mr McGuigan’s death.
Det Chief Insp John McVea said police searches took place in various parts of Belfast.
As part of the investigation, two guns were found in the greater Belfast area.