Slain Real IRA terrorist Alan Ryan was under investigation in relation to serious crime on both sides of the border, it emerged last night.
Police are linking him to incidents, including a murder, that are believed to have been organised by the Real IRA faction in Londonderry.
Ryan is believed to have developed strong links with several dissident activists in the north west after his release from Portlaoise jail in the middle of the last decade.
And he maintained a close relationship between his Dublin-based gang and the leadership of the Derry faction, particularly after being involved in a major row with the terrorists' 'commander' in Dublin.
Ryan was thought to have used his 'muscle' to help the Derry terrorists with some of their operations.
Within hours of his murder on a Dublin street, the Derry branch of the 32 County Sovereignty Movement, alleged to be the political wing of the dissident group, paid tribute to Ryan on a website.
It referred to the "cowardly murder of our friend, comrade and activist" and said words could not express the pain felt by the movement and individual activists at his death.
The message also referred to Ryan's work as an ex-republican prisoner, campaigning for his comrades in Maghaberry jail in Northern Ireland.
The 'professionalism' of the shooting of Ryan has prompted gardai to put some credence in an intelligence report indicating that a hitman had been brought in from outside the Republic of Ireland to murder him.
Officers said the gunman appeared to have been exceptionally cool as he walked up behind Ryan and two friends at Grange Lodge Avenue in Clongriffin, on the northside of the capital, on Monday afternoon.
After shooting Ryan in the back and legs with a 9mm handgun, the shooter stepped up to his victim's body on the ground and fired a bullet into his head.
Some officers said the shooting was reminiscent of attacks carried out by terrorists during the Troubles.
But investigators think it is likely that the hit was sanctioned by an organised crime gang rather than dissidents that had clashed with Ryan.
Ryan's group is thought to have been responsible for at least two murders in Dublin, the shooting of criminal Sean Winters in Portmarnock in September 2010, and last September's gunning down of leading gangland figure, Michael "Mica" Kelly, also in Clongriffin.