Perth father killer not guilty of murder

A Perth man who fatally stabbed his 50-year-old father and told police afterwards he had been hearing voices in his head has been found not guilty of murder because he was of unsound mind.

William Mathrew Rigden, 26, rushed into John Clayton Rigden's Armadale home in May 2016, pushed him against a wall and stabbed him in the chest and neck.

Rigden then ran out of the house and was followed by family members who wrestled with him and hit him with a baseball bat.

He told police who interviewed him in hospital the voices in his head were relentless and angered him until he wanted to hurt himself or someone else.

Rigden said he resented his father, who had called him a bastard since he was a child, and only only wanted to hurt him but "must have took it too far".

He also said he was glad his father was dead, "looking back at what he's done", but realised he wouldn't stop hearing his voice.

Rigden faced a brief judge-alone trial earlier this month.

"I am satisfied that it is more likely than not that the accused was in a psychotic state at the time he caused the death of his father," Supreme Court of WA Justice Stephen Hall said in his judgment on Thursday.

"That psychotic state was likely to have been of such a nature and intensity as to deprive the accused of the capacity to know that he ought not to do the act that caused the death of his father.

"Accordingly, the accused cannot be considered criminally responsible for his actions."

The court heard Rigden began to experience auditory and commanding hallucinations at the age of 14 and has heard them almost continuously since then.

Rigden will be detained indefinitely in a psychiatric facility under a custody order.