Gardai have arrested two men in connection with yesterday's gangland-style execution in Dublin's north inner city.
One of the men, a 33-year-old from the Ballymun area of the city, turned himself to gardaí at Fitzgibbon Street last night.
The second man was also detained overnight and is believed to be in his 40s, but gardaí have not released details of where and how he was arrested.
The pair are being questioned about the murder of 31-year-old Mark Byrne, who was shot dead near the Mater Hospital yesterday morning just minutes after being let out of Mountjoy Prison on day release.
Gardaí are investigating the possibility that the killing may be linked to a dispute between the dead man and another inmate inside the prison.