Mark Ludbrook, 54, turned a knife on Autumn Baker on August 3, 2023, stabbing her to death in his Melbourne home while under the influence of illicit drug PCE.
Ludbrook had taken the substance to manage pain from a rare neurological condition, and argued at trial he was not conscious of his actions because the drug had altered his mind.
But a Victorian Supreme Court jury rejected that assertion, finding Ludbrook consciously, deliberately and intentionally murdered Ms Baker, who was aged 40.
The attack was frightening and horrible but it was clear Ludbrook's ability to reason had been severely impacted by the drug, Justice James Gorton said on Thursday.
"It explains what is otherwise entirely inexplicable behaviour," the judge told the court.
Justice Gorton found Ludbrook's moral culpability was significantly moderated as he sentenced the 54-year-old to a maximum of 19 years behind bars.
With time already served, Ludbrook will be eligible for release on parole in just 12 years.
Ludbrook, who watched the sentence on a video link from prison, did not react as he learnt his fate.
Inside the courtroom, Ms Baker's family and friends shook their heads, while some wiped away tears.
Twenty victim impact statements were previously submitted to the court, which Justice Gorton said showed Ms Baker was a kind, generous and much-loved woman.
The judge noted that, even in her final moments, Ms Baker had sought to assist a friend.
"She had done nothing to provoke you and was only trying to help," Justice Gorton told Ludbrook.
The judge described the case as "most unusual", noting how wheelchair-bound Ludbrook had walked around naked for more than an hour before the murder.
He also told his carer Amber Davison she needed to sleep with him to save the animals.
"(Ms Davison) had found your behaviour unsettling," Justice Gorton said.
Ludbrook then grabbed a knife from the kitchen and was stabbing himself in the stomach when Ms Baker tried to pull the weapon away from him.
He instead turned it on her and repeatedly stabbed her to the chest, arms and eyes.
Justice Gorton found, while Ludbrook was conscious of his actions, it was clear the drug had made him behave bizarrely and violently.
The judge noted Ludbrook had previously taken illegally-sourced ketamine to manage his pain without issue, but it was the first time he had consumed PCE.
There was little information about the drug's affects so there was no way for Ludbrook to have anticipated what happened next, Justice Gorton said.
"It is not an excuse ... but it is relevant," the judge said.
The drug impacted Ludbrook's reasoning, so his moral culpability should be viewed as significantly moderated, Justice Gorton found.
The 54-year-old had also shown remorse and was very regretful for his actions, Justice Gorton accepted.
The judge considered Ludbrook's rehabilitation prospects as good and said his time in prison would be more difficult due to his neurological condition.
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