A man who believed he had "special powers to identify paedophiles" has been found not guilty of murdering a complete stranger at a Perth bus stop on the grounds he was "not of sound mind" at the time.

Key points: Ian Baz-Bosch died three days after he was stabbed by Ben Daly in Coolbellup

Ian Baz-Bosch died three days after he was stabbed by Ben Daly in Coolbellup Mr Daly's lawyers said he did not have the capacity to control his actions at the time

Mr Daly's lawyers said he did not have the capacity to control his actions at the time A "custody order" means Mr Daly will be kept at a psychiatric facility indefinitely

Ben Cedric Daly fatally stabbed Ian Baz-Bosch in the southern suburb of Coolbellup about 7:30am on November 19, 2016.

Mr Baz-Bosch was on his way to the shops to buy a card and a fruit platter for his young son to take to a birthday party later that day.

His last movements were captured by CCTV cameras on the buses he caught and at a nearby shopping centre.

Ian Baz-Bosch had never met Mr Daly before the fatal attack. ( Supplied )

He was stabbed in the neck and died three days later in hospital.

The not guilty verdict does not mean Mr Daly will be released because he will be subject to "a custody order", meaning he will be kept at a psychiatric facility indefinitely for treatment.

In his decision, Justice Joseph McGrath said he "was satisfied on the balance of probabilities" that at the time of the stabbing Daly was "mentally impaired".

"Consequently he was deprived of the capacity to know that he ought not do the act [the stabbing] and the capacity to control his actions," he said.

"Accordingly, Mr Daly is not criminally responsible for his actions by reason of unsoundness of mind."

Killer's house bugged by police

Mr Daly was a suspect from early on in the police investigation into Mr Baz-Bosch's death, but was not charged until four months later.

Ben Daly believed he had "special powers to identify paedophiles". ( Facebook: Ben Daly )

As part of what was described in the Supreme Court as a complex investigation, police bugged Mr Daly's home and recorded him talking about "hunting and killing paedophiles".

His lawyers maintained he should not be held criminally responsible for the crime, arguing that at the time he stabbed Mr Baz-Bosch he was deprived of the capacity to control his actions.

Mr Baz-Bosch was on his way to the shops when he was fatally stabbed. ( Supplied )

Mr Daly had a history of mental illness and was diagnosed with psychosis in October 2012 after he reported hearing voices. Two years later he was diagnosed with schizophrenia.

But prosecutors argued Mr Daly should be found guilty of murder because he was also a user of cannabis and amphetamines and had a record of not taking his medication.

Angels told Daly about paedophiles: psychiatrist

A psychiatrist who testified at the trial, Victoria Pascu, said when she interviewed Mr Daly after he was charged, he told her he had special powers to pick out paedophiles by looking at them and that he had been recruited by a bikie gang to "save the kids".

Mr Daly will likely be kept at a psychiatric facility indefinitely for treatment. ( Facebook: Ben Daly )

Dr Pascu said it was her opinion that when Mr Daly stabbed Mr Baz-Bosch he was driven by psychosis, which included hearing voices from angels which she suspected might have been telling him who the "paedophiles" were.

She concluded he was deprived of the capacity to control his actions and to know that he ought not stab Mr Baz-Bosch.

But another psychiatrist testified he did not believe Mr Daly was deprived of any of his capacities because he had not given an account of what happened on the day, including what he was thinking, how he was feeling and his perceptions of the world.

System 'seriously wrong', victim's wife says

Mr Baz-Bosh's wife, Emerald Baz, fought back tears outside court, saying while nothing could ever make things better for her husband's family and friends, they were pleased Mr Daly had been removed from the community.

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 2 minutes 24 seconds 2 m 24 s Emerald Baz speaks about her husband's death

She also called for more funding and resources to be allocated to mental health services.

"It took the murder of an innocent person, Ian, for Ben to be removed from the community and receive treatment. There is something seriously wrong with the system," she said.

"What was very apparent whilst we sat through the trial is that there is a huge lack of resources and funding in the mental health services to deal with individuals like Ben.

"He was someone who was identified as a risk of harming himself and others, receiving what I believe was referred to as aggressive treatment where he occasionally was visited in his home by mental health services.

"Sadly this wasn't enough and he really was not receiving the adequate treatment that this condition required.

"I have to add this is not an isolated incident and it won't certainly be the last as long as mental health services remain as they are."

Ms Baz described her husband as a sympathetic person who would have reached out to try to help someone like Mr Daly.

"It's been a long, emotionally draining three years and we're glad it's finished," she said.