The family of a paranoid schizophrenic wanted to get psychiatric help for him in the weeks before he killed his parents with an axe, the Central Criminal Court has heard.

43-year-old Julian Cuddihy has pleaded not guilty by reason of insanity to the murder of his parents Kathleen, 73, and James, 77, at their family home in Churchtown, Carndonagh, Co Donegal on 22 October 2014.

Detective Garda Bernard Mullins of Buncrana Garda Station told prosecuting counsel Denis Vaughan Buckley SC that James Cuddihy cancelled an appointment his son had with local mental health services six days before the violent episode.

Consultant psychiatrist Dr Damian Mohan gave further evidence that Mr Cuddihy's parents were concerned about the stigma associated with mental health.

Speaking to defence counsel Brendan Grehan SC he said that Ms Cuddihy in particular did not want him to be committed and worried that he would resent them if they had him hospitalised against his will.

At that time Mr Cuddihy was refusing to eat because he believed his mother was trying to poison him.

He could not sleep because he worried that people were stealing his thoughts while he slept and he believed he could prevent aliens from reading his mind if he joined the IRA.

He had become convinced that people were conspiring against him and had taken to sleeping in an annex attached to the family home with an axe for protection.

His symptoms had been building for several years and in December 2013 the family met their General Practitioner to discuss the possibility of having him committed but, Dr Mohan said, the decision was deferred.

By October 2014 his behaviour was so erratic that his siblings felt he needed immediate psychiatric help but his parents resisted enforced committal to a psychiatric unit.

Dr Mohan said the parents shared their family's concerns but "did not want to follow through. They wanted to be protective of their son but also did not want him to be submitted to a mental health facility."

Dr Mohan said the family is extremely unified and loving and only ever wanted what was best for Mr Cuddihy but he added that mental illness is treatable with early intervention.

"Hindsight is a fine thing," he said, adding that Mr Cuddihy has made strong progress since being committed to the Central Mental Hospital following the attack on his parents.

Detailing the nature of Mr Cuddihy's delusions, he said he spoke to him about what he believed in the days and weeks leading up to the attack.

He said Mr Cuddihy heard voices telling him what to do and believed that he was going to be taken away by aliens to the Matrix, referring to the Keanu Reeves film in which reality is simulated by a computer.

He said his thoughts were confused and hard to piece together.

He sometimes believed his mother could read his thoughts and at other times that birds could steal his thoughts.

He had notions that the IRA was trying to recruit him and this somehow tied in with the idea that aliens were reading his mind and that he was going to be taken to the matrix.

His paranoia led him to believe that people were conspiring against him and that his mother was trying to poison him.

Two nights before the killing he had stayed out in one of the fields near their home believing that aliens were going to take him away to another dimension.

He waited all night and was "greatly disappointed when the spaceship did not arrive".

On the night of the killing he said his mother had told him to eat his dinner and he then heard her voice in his head.

She told him: "I want you to kill me and your father." He believed that by killing them he was sending them to heaven and when he attacked them with the axe he thought he was following his mother's commands.

Later that night, as he wandered through fields near the family home he became convinced that he was in the matrix, an alternative reality, and that he therefore had not really killed his parents.

Det Gda Mullins had earlier confirmed details from the State Pathologist Professor Marie Cassidy's report into the deaths of Mr and Ms Cuddihy.

Professor Cassidy described multiple wounds to the head consistent with blows from an axe that caused severe head trauma.

She also discovered stab wounds to Mr Cuddihy' neck, chest and face that she believed could have been caused by a pair of scissors that were found close to his body.

Ms Cuddihy had suffered at least seven blows to the head, some of which she believed were inflicted while she was lying down unconscious or possibly already dead.

Det Gda Mullins also recalled an interview with Mr Cuddihy at Buncrana Garda Station on 24 October, two days after the double killing.

Speaking to Mr Buckley, he said that during the interview gardaí asked Mr Cuddihy if he knew what would happen when he struck his parents with the axe.

He responded: "I believed their lives were going to pass on to the unifying field. I knew they were going to die. When the switch turned on I knew they were going to die," he said, adding that he did it "as quickly and painlessly as possible".

The trial continues tomorrow in front of Justice Margaret Heneghan and a jury of seven women and five men.