Gardai were searching last night for John Gallagher (33) who killed two women in 1988 and who failed to return to the Central Mental Hospital from parole on Saturday.
Gallagher is not considered to be a danger, according to Dr Charles Smith, clinical director of the Central Mental Hospital.
He has been leaving the hospital unaccompanied to go to work for the past two years.
That Gallagher would get longer and longer periods of freedom from the hospital was anticipated by the High Court in 1996, when it turned down his application for his immediate release.
Gallagher was found guilty but insane in 1989 of the killing of his former girlfriend, Ms Anne Gillespie - who had ended their relationship - and her mother, Annie, outside Sligo General Hospital the previous year.
The East Coast Area Health Board said Gallagher had left the hospital "for a pre-planned social outing". He was due to return by 7 p.m. but failed to do so.
"For the last five years, Mr Gallagher has been following a phased rehabilitation programme, the completion of which would have ultimately led to his discharge from the hospital," it said.
The programme included "unaccompanied parole to work in a normal environment for a commercial employer for the last two years".
Since last October he has been living in a hostel in the grounds of the hospital as part of a phased pre-release programme agreed with the Department of Justice. "He has fully complied with all aspects of the programme and was being granted increasing levels of freedom in preparation for his eventual discharge," yesterday's statement said.
Gallagher's detention and treatment have been monitored by an advisory committee, made up of a barrister, psychiatrist and GP, which was set up in 1991.