Tommy Crossan, 43, was shot several times while he sat in an office in the grounds of an industrial complex off Springfield Road in West Belfast.
A 26-year-old man was arrested by the Police Service of Northern Ireland yesterday in connection with the killing of the father of six, who was a former senior member of the Continuity IRA.
Detective Superintendent Jonathan Roberts said: "The murder of Mr Crossan on the Springfield Road was a brutal and ruthless attack which has no place in society. Mr Crossan was known to police but no matter what his lifestyle was, absolutely nothing justifies this barbaric action against him."
The killing was also condemned by Northern Ireland's First Minister Peter Robinson.
He said: "The small minority of people who want to continue terrorising the community need to understand that they will not be allowed to drag Northern Ireland back to the dark days of the past."