Exactly what happened may never be known.
"It is not possible to be precise about the nature of the altercation as [the man's] recollection of events that day is inconsistent with the forensic evidence and could be be tainted by delusions induced by his mental illness," Justice Williams' judgment says.
What is known is that the man struck Ms Stewart above her right eyebrow, causing her nose to bled.
He then began strangling her.
Ms Stewart clawed at his chest, injuring him, but the strangulation continued, either causing her to lose consciousness or perhaps killing her.
But the man continued the attack, grabbing a knife and stabbing Ms Stewart in the chest seven times, puncturing her lungs and aorta, the body's main artery, as well as fracturing ribs.
Finally, the man stabbed Ms Stewart in the neck, severing the jugular vein.
"The knife was left in situ," Justice Williams says.
The man then washed his hands and changed out of his bloodstained clothes, before he confessed his crime to an ex-girlfriend and a cousin, who contacted him.
From the outset he accepted what he did, but after hearing expert evidence at last week's hearing, Justice Williams concluded he was not guilty because of insanity.
"Evidence from eminent experts of long experience provides ample support for a conclusion that [the man] was insane when he killed ... ," the judge says.
"His delusional state was such that, on the balance of probabilities, he did not know that what he did was morally wrong, even if, on the evidence, he clearly understood what he was doing and the likely result."
The man will be detained as a special patient in a psychiatric hospital.
