A fifth man being questioned about the murder of Robbie Lawlor (36) in Belfast last weekend has been released from custody.
It means all five suspects detained on suspicion of the gangland criminal's fatal shooting in Ardoyne just before noon last Saturday have been released without charge.
The first three suspects arrested, including a 17-year-old, are linked to members of the McCarthy-Dundon gang in Limerick. The PSNI believes they travelled with Lawlor to north Belfast on the day he was killed.
They were intending to enforce a drugs debt but Lawlor was instead shot by a killer who appeared to have details of his movements in advance.
A 27-year-old man from the North and with links to dissident republicans was also arrested in Crumlin, Co Antrim, on Sunday. The fifth suspect was arrested in north Belfast on Tuesday night and was released on Thursday.
Gardaí and the PSNI are trying to establish if the killing of Lawlor is linked to a drugs debt row in Belfast or is linked to a gang feud in Drogheda, Co Louth, which he was involved in; or perhaps a combination of both motives.
Lawlor, who was from north Dublin but had lived in Laytown, Co Meath, for a period, was a suspect for the most recent killing in the Drogheda feud, that of Keane Mulready Woods in January.
The 17-year-old was abducted and murdered in Drogheda before being dismembered. His remains were found in different locations in north Dublin in the days following his disappearance.
Lawlor was suspected of involvement in a number of shootings, some of them fatal, linked to the Drogheda and Dublin organised crime scenes. He had been warned his life was in danger from the Drogheda faction that shot dead his brother-in-law Richard Carberry last November.
And gardaí had also warned him his life was in danger as a result of a dispute he was involved in with a significant gangland figure from north Dublin. That feud resulted from Lawlor's suspected role in the murder of Dubliner Keith Finn in Darndale, north Dublin, two years ago.
Despite arresting and then releasing five suspects to date and carrying out searches at several properties, the PSNI has not yet found the firearm used to shoot Lawlor on Etna Drive, Ardoyne.
The PSNI believes the killer had very extensive local knowledge of the area and that he escaped, to a waiting car later found burnt out, through a house close to the murder scene.