Although urged by the coroner to remain, the man walked out of Sligo court, insisting he had an urgent appointment elsewhere.
Relatives of the deceased man, Cyril Moran, who was beaten to death, were stunned.
His first cousins, Anthony Monaghan, Joe Moran, and Kathleen Moran, who were clearly upset by the evidence, said they were seeking closure and now would have to return for a resumed hearing.
Mr Monaghan said: “It was very harrowing what we heard. When the juror walked out it was just terrible.”
The relatives two years ago complained that the attacker, Daniel McLoughlin, should have been given a 10-year-sentence instead of five for assault causing serious harm.
Mr Monaghan said: “We still feel his sentence should have been doubled, especially after what we heard today.”
The inquest into the death of 60-year-old Mr Moran lasted less than 55 minutes before the jury of six retired to return a verdict.
At that stage one of them, who five minutes earlier told the coroner he had an urgent appointment elsewhere, walked out of the court as the other five retired to a rear room. Coroner Eamonn MacGowan said he had to have a minimum of six on the jury but the man continued on his way.
Coroner’s clerk Sgt Phil Maree followed the runaway juror out of court but moments later returned without him.
At that stage the coroner said it was his “unpleasant duty” to adjourn the hearing and resume it at the earliest date.