Prison staff did not warn colleagues an inmate was on suicide watch before he was found hanged in a courthouse holding cell, a report has found.
Shane Rogers was on remand at Cloverhill Prison, Dublin, in December 2011 for killing Crossmaglen GAA star James Hughes when he died.
A report by Judge Michael Reilly, Inspector of Prisons, found Rogers had not been monitored for almost an hour after a court appearance.
The inspector said it is clear that prison staff charged with escorting and detaining Rogers at holding cells in the prison-linked courthouse had not been told about his vulnerable state of mind.
Rogers had admitted killing Mr Hughes while in custody and was assessed as a suicide risk.
The report said there were a number of deficiencies including a failure of prison staff to communicate with each other, failure to adhere to stated work practices, an absence of governance to ensure compliance with standard procedures and inadequate record keeping.
Rogers, 32, of Deery Terrace, Inniskeen, Co Monaghan, was involved in a row with Mr Hughes before he killed him with one of his legally held firearms in the early hours of December 11, 2011.
He had twice punched Mr Hughes, All-Ireland club medal-winning captain of Crossmaglen Rangers, from Co Armagh, after seeing him with his ex-girlfriend Patricia Byrne in a Dundalk nightclub.
Mr Hughes was shot and died, while Ms Byrne and taxi driver Anthony Callan were injured when Mr Rogers opened fire after the cab pulled up outside her Dundalk house.
Justice Minister Alan Shatter said: "I would like to express my sincere sympathy to the family of the late Mr Rogers and indeed to all of those affected by this tragic case, in particular the family of the late James Hughes," the minister said. "I hope this report, which regrettably has identified some system failures, will help to clarify matters for them."