Ian Dennis Jones, 52, found not guilty of murder, will remain in psychiatric facility indefinitely

A man who strangled a mother-of-three at his home in Western Australia's south and was then seen wandering naked on a highway has been found not guilty of murder because he was of unsound mind at the time.

Ian Dennis Jones, 52, went on trial before a Supreme Court of WA judge sitting without a jury earlier this month, admitting he caused the death of a woman at his Bunbury house in November 2016.

However he argued he was not culpable because he was of unsound mind.

The court heard the victim, 41-year-old Tanya Beattie, had become an alcoholic and started using drugs after she lost her job as a registered nurse, accused of stealing morphine.t

She would wander the streets drunk, talking to strangers, and became "drinking buddies" with Jones, who lived on the route she took to visit a friend.

Her husband Danny Beattie said she initially described Jones as a "cool guy" but eventually labelled him "a nutter".

Jones had a long history of mental illness and behaved bizarrely in the weeks before the killing, forming the belief Ms Beattie was a member of a bikie gang he blamed for his son's death.

After being "spooked" by Jones, Ms Beattie told her husband she wouldn't visit him anymore and would avoid walking past his house, but they were seen arguing outside the property on the night she died.

A neighbour heard a scream about four hours later.

The next day, after being seen splashing in mud and talking nonsensically, Jones was spotted walking naked down a highway.

Police were called, he was taken to hospital and Jones' mother found Ms Beattie's body when she went to his house to lock up.

Justice Lindy Jenkins handed down her verdict on Monday, saying Jones' mental impairment deprived him of the capacity to control his actions and ordered he be detained indefinitely in a psychiatric facility under a custody order.

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