A former Tyrone GAA player told a psychiatrist that killing a parent so they could look over him in heaven was a "cover-up" and "an excuse", a court has heard.
The alleged admission from Sean Hackett was revealed as it emerged experts disagree on whether he was suffering from an abnormality of the mind.
Hackett admits he intended to kill his father Aloysius when he shot him dead at the family home near Augher last January.
But the 19-year-old, a former captain of the county's minor team, denies murder and two counts of possessing a firearm with intent to endanger life.
The court has previously heard how, weeks before he shot his father, Hackett attempted to strangle his mother Eilish with a television cable.
Mrs Hackett said her son told her he wanted her to be in Heaven to look after him.
Yesterday, the court heard Hackett told a psychiatrist, Dr Fred Browne, that he "didn't really believe" that.
He allegedly told the expert that he "felt this would be a good cover-up", also saying: "I nearly made myself believe it."
However, psychologist Dr Philip Pollock said he was "bothered by the word cover-up", and suggested it could all be a question of interpretation.
He said he didn't think "the Heaven line" was a cover-up. Dr Pollock also rejected the suggestion Hackett had attempted to "pull the wool over everybody's eyes".
The court was told that Dr Pollock and Dr Browne have reached contrasting conclusions on Hackett's mental state.
Under cross-examination by prosecuting counsel Ciaran Murphy QC, Dr Pollock said there was evidence of "extensive preparation" from the accused in the build-up to the shooting of his father. This included borrowing the gun as far back as October – three months before the killing – and having practice sessions in the mountains.
"There is lots of evidence of extensive, deliberate planning," Dr Pollock conceded.
The court heard Hackett had exercised self-control "four or five times" on January 4 last year – the day he shot his father.
He had hid behind a wall as his mother returned home from work.
Later, he was in his room with the gun, considering ambushing her as she exited the shower. On both occasions Hackett did not follow through with his plans.
However, that night he killed his father by shooting him twice in the head.
Dr Pollock said the defendant told him he was "getting myself revved up to shoot dad".
Hackett also told him: "I felt excited I was going to do it. It felt powerful."
Dr Pollock did not believe that he felt pleasure or enjoyment in carrying out the killing, but instead relief and release that his depression would be resolved.
The psychologist was asked why Hackett was able to exercise self-control prior to going actually through with the shooting.
He replied: "There is rational decision-making all the way through the planning but it doesn't mean it isn't driven by irrational belief and motivation."
Earlier, Mr Murphy put it to him that Hackett was acting perfectly normal on the day of the killing, saying he was "smiling and well-mannered".
Dr Pollock replied: "Externally yes... internally we're getting a picture of something different."
Later, when asked whether Hackett "got a kick" out of killing his father, Dr Pollock replied: "I don't think those are the words I would use."
Sean Hackett is accused of shooting his father Aloysius dead with a borrowed rifle.
His trial has already heard that he had reloaded the rifle and shot his father again.
His mother also gave evidence he had tried to strangle her with a cable, telling her that he wanted her to go to Heaven to watch over him.
He told police he was suffering from depression.