An Adelaide man charged with a screwdriver stabbing murder has been found not guilty with a Supreme Court judge ruling he was mentally incompetent at the time.
William Robert Delany, a diagnosed schizophrenic, stabbed Nathan Clark several times at a home unit at suburban Elizabeth in August 2019.
His defence argued that while he inflicted the fatal injuries, he was deeply psychotic during the attack.
Prosecutors conceded he was mentally incompetent at the time, but argued his psychotic episode was substantially self-induced by his methylamphetamine use.
On the day of the murder, Delany had consumed meth at least three times and was described by witnesses as "wigging out", agitated, and "roaring".
But in a judgment on Thursday, Justice Kevin Nicholson found that the Crown had failed to prove that Delany's mental incompetence was self-induced.
"The expert evidence supports the following, fundamentally relevant, propositions," he said.
"First, it is not possible to distinguish between a psychotic state caused by schizophrenia and one caused by self-induced intoxication simply by analysing the patient's mental state and consequential conduct at any given time.
"Second, whilst methylamphetamine consumption can cause either a relapse of a psychotic state or an exacerbation of a psychotic state in a person suffering from schizophrenia, there is no way of knowing whether either has happened, as opposed to the schizophrenia having simply run its course."
Justice Nicholson ordered Delany be held in a secure mental health facility until further order.
Had the prosecution's argument on self-induced psychosis prevailed, the 32-year-old would have been liable to a jail sentence.
