A man with paranoid schizophrenia used five knives as he killed two pensioners in their own home in a "gratuitous, sustained and frenzied attack", a court has heard.
Thomas Scott McEntee, 41, stabbed husband and wife Michael and Marjorie Cawdery, both 83, multiple times when they returned from their weekly shopping trip to find him committing a burglary.
Mr Cawdery was also beaten by McEntee and there is evidence he was conscious when some of the injuries were inflicted, Belfast Crown Court heard.
A sentence hearing before Mr Justice Adrian Colton was told the couple's daughter Wendy discovered the bodies of her parents after the indiscriminate attack at the property in Portadown, Co Armagh, in May last year.
In a victim impact statement read to court, she said the entire family had been left "devastated" by the loss of their "mainstays".
McEntee, who was arrested in a nearby field of cattle hours after he killed the pensioners, has pleaded guilty to manslaughter on the grounds of diminished responsibility.
Both defence and prosecution agree he was suffering from acute mental illness when the incident took place.
They also agree McEntee does not need to serve his sentence in a hospital setting, and should instead go to prison.
However at Friday's pre-sentence hearing, the lawyers were at odds over how aware McEntee was of the acts he perpetrated.
Defence barrister Kieran Mallon QC insisted his residual culpability was minimal, given his "extremely disturbed mental state".
But prosecutor Peter Irvine QC argued that his level of culpability was at the higher end of the scale, noting that he had taken actions to conceal the crime, such as pulling window blinds and changing clothes.
McEntee, whose previous address was given as the Simon Community, Moorfield Court, Kilkeel, Co Down, but who is currently being held at a secure mental health facility, sat impassively in the dock wearing a white shirt and flanked by healthcare workers.
Mr Irvine told the judge that the victims' vulnerability was an aggravating factor.
"The attack against them was gratuitous, clearly sustained and frenzied in nature," he said.
The court was told of McEntee's erratic behaviour in the period before the attack.
The day before, he was reported to police amid claims he was making a nuisance in the main square in Warrenpoint, Co Down, and approaching women.
Officers picked him up and left him at Newry train station.
That night he broke into a van and slept in it.
The next day he called at his sister's house in Bessbrook, Co Armagh, at 6.30am - the first time she had seen him in a number of years.
After leaving there he was reported as being naked in a public place in nearby Camlough.
He was taken to Craigavon Area Hospital after expressing suicidal intentions and exhibiting a wound on his arm.
However, he left the hospital before a full assessment had been carried out, stole a bottle of wine from a nearby off-licence and less than 90 minutes later stabbed the couple in their Upper Ramone Park home.
The court was told McEntee had no recollection of the event when he was arrested in the field wearing Mr Cawdery's jacket.
The killer, who had also stolen and crashed the couple's car, told officers all he could remember was patting cows.
Mr Mallon said his client had since expressed remorse, indicating he was "acutely live to the considerable distress and grief" he had caused the Cawdery family.
The defence lawyer hailed the "consummate dignity" of the family and proceeded to read out a number of victim impact statements.
First, he read out Wendy Little Cawdery's: "My mum and dad were the mainstay of our family and always there willing to help and support the younger generation in whatever way they could.
"We have prematurely lost their all-important guiding influence which has had a devastating impact on the family as a whole."
The lawyer then read a statement from Mr Cawdery's brother Padraig.
Mr Cawdery said his brother was "beloved by all and a model of compassion and humour" and said the deaths had left a "void that could never be filled".
Judge Colton discussed with the lawyers the sentencing options open to him to impose, including a discretionary life term.
He said he would take time to consider all the issues raised during the two-hour hearing and pass sentence next Thursday.