Gardai are investigating a report indicating that a hitman was hired from abroad to murder dissident terrorist Alan Ryan.
Officers have described the shooting of Ryan (32), a leading member of the Real IRA in Dublin, as professional.
Ryan was strolling along a quiet street with two friends when he was targeted.
The gunman walked coolly towards Ryan from behind.
He opened fire with a 9mm handgun and hit Ryan in the body and legs, bringing him to the ground, before directing another bullet into his victim's head.
A companion was shot in the leg but the other escaped injury. The gunman then jumped into a getaway car, a silver Volvo driven by an accomplice, and made off.
The Volvo was later found burnt out at the Hole in the Wall Road.
Although Ryan and his faction were in dispute with the Real IRA ‘commander' in the capital, officers think it more likely the hit was ordered by a criminal gang.
One Garda said last night that Ryan had so many enemies that police could not draw up a shortlist of likely suspects.
A tribute was placed yesterday on the website of the 32 County Sovereignty Movement, placed by its Derry branch.