A 26-year-old man has been arrested in connection with the murder of former dissident republican leader Tommy Crossan, who was shot dead in west Belfast on Friday.
The 43-year-old ex-Continuity IRA (CIRA) figure was gunned down at a fuel depot in the grounds of an industrial complex in full view of surrounding houses.
The Police Service of Northern Ireland (PSNI) said the man was arrested in Belfast by officers from its Serious Crime Branch and is being questioned at a police station in Antrim.
It is believed up to three gunmen may have carried out the killing. A red BMW was found set alight nearby - the area has long been known as a republican heartland but has been relatively peaceful in recent years following the end of the IRA campaign in 1998.
Distressed relatives gathered at the scene and a priest attended to pray over the victim
Belfast City Council Lord Mayor Mairtin O Muilleoir, of Sinn Fein, spoke out to condemn the killing.
He said whoever was behind the killing had no support in their attempts to backtrack on the progress made in the city: “They are dinosaurs trapped in the past and I urge everyone to work with the police to remove them from our streets.”
Crossnan was once the CIRA's Belfast leader but was believed to be the subject of a death threat and had been expelled from the group some years ago after a fall out.
He spent time in jail for conspiracy to murder Royal Ulster Constabulary (RUC) officers following a gun attack on a police station in west Belfast in 1998.
The CIRA has opposed the peace process which largely ended three decades of violence and transformed Northern Ireland. Crossan was killed on the 16th anniversary of the Good Friday Agreement which mandated political power-sharing at Stormont.
CIRA gunmen murdered Police Constable Stephen Carroll in Lurgan in Co Armagh in March 2009 but the organisation has since been riven with splits, security sources have suggested.
Friday afternoon's attack happened at the Peter Pan Centre in Springfield Road, the (PSNI) said. Detectives have launched a murder investigation and are combing the scene for forensics clues.
Mr O'Muilleoir told BBC Radio 4's The World Tonight: “There are some micro groups of criminals masquerading under an assortment of republican labels. They have no support within the community.”
The area of Belfast where the shooting happened is mainly comprised of tightly-packed terraced housing estates and businesses.
Nationalist SDLP councillor Colin Keenan said it was a horrific scene.
“We have long hoped that the shadow of death had been lifted from west Belfast.
"Today's event is a terrible, tragic reminder of the violent conflict of the past."
Stormont Justice Minister David Ford also condemned the shooting.
Members of the security forces have been on high alert for attacks by various extremist factions who have also killed two soldiers and a prison officer.
In recent weeks they have stepped up efforts to kill police officers, with several attacks on the force in west Belfast.
After the murder of prison officer David Black on the M1 motorway in November 2012, police mounted an unprecedented surveillance operation against various factions as well making significant arrests.
Additional reporting by Press Association