First he drugged university student Jun Lin with sedatives, killed him and then repeatedly mutilated his body.

Next, Luka Magnotta lugged the limbs and torso to a trash heap outside his Montreal apartment and mailed some of the body parts across the country, a courtroom has heard over the past 10 weeks.

Then he booked a flight to France.

And now, with the case in the hands of the jury, it comes down to whether the apparent choreography and certain gruesomeness of those acts add up to a cold-blooded murderer, or a young man in psychiatric distress.   

The defence strategy in the Montreal courtroom has been straightforward since Day 1: Agree to the basic underlying acts, but show that Magnotta suffered from paranoid schizophrenia that made him either unable to appreciate what he was doing or that it was morally wrong.

Meanwhile, the prosecution has suggested the former porn actor was faking symptoms and had meticulously plotted the killing months in advance.

Whose version jurors will accept, and whether they return a verdict of guilty or of not criminally responsible (NCR) by way of mental disorder, depends on five key factors.

1. Grotesque, but psychotic?

In some ways, prosecutor Louis Bouthillier has faced a delicate balancing act. To secure a conviction for first-degree murder, which requires proving planning and deliberation, he's had to pull back the curtain on Magnotta's behaviour in the years and months before he met Lin. That behaviour was often grotesque, even sadistic, such as allegedly suffocating cats and posting videos of it online.

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The defence has to prove Magnotta was so mentally disturbed he either couldn't appreciate the nature of his actions when he killed Jun Lin, above, or couldn't tell it was morally wrong. (CBC)

And then during trial, Bouthillier introduced copious, gruesome evidence of how Magnotta killed and dismembered Lin.  

It all risks playing into the defence's hand, according to some experts. The more macabre Magnotta seems, the more the jury might be willing to accept his insanity plea.

"That's a problem the prosecutor does have. If you have somebody who does something so bizarre, the average person might say, 'This person must be disordered,'" said John Bradford, one of Canada's top forensic psychiatrists.

On the other hand, the more evidence that Magnotta is a dangerous killer, the less likely jurors might be to opt for an NCR finding and the usually ensuing psychiatric hospitalization — which sometimes only lasts a few years.

"Any jury in Canada now would know that he gets reviewed periodically and may at some point be returned to the community," said Patrick Baillie, a forensic psychologist and lawyer in Alberta who has consulted on NCR cases for more than two decades. "Whereas if he's found guilty of murder, he may get locked up for a long period of time."

2. Duelling psychiatrists

The testimony of the six psychiatrists who assessed Magnotta in one way or another will weigh heavily with the jury. Four of them testified for the defence, including two as expert witnesses who between them spent 63 hours with Magnotta. Their shared conclusions were that he suffered from schizophrenia and bouts of psychosis.

The prosecution called two psychiatrists, one who assessed Magnotta for just an hour and theorized he had a possible personality disorder but not psychosis. The other, the prosecution's expert forensic psychiatrist, never met Magnotta at all — but that was because the accused refused to submit to examination. And that could undermine all the defence's experts.

"That doesn't play well for a jury," said Greg Brodsky, a veteran Winnipeg lawyer who has won two major NCR cases at the Supreme Court of Canada. "What are you hiding?"

3. Contested designation

The surest path to a finding of not criminally responsible, a number of observers said, occurs when the expert witnesses for the prosecution and defence both agree on the designation. "In 22 years I've been practising here, there hasn't been a single successful case where it was a battle of experts," said Baillie, the Calgary forensic psychologist. "If the prosecutor's expert has said it's not NCR, then the courts have found not NCR. If the prosecution's expert said it is, then that's the end of the process."

Roy O'Shaughnessy, a professor and former head of forensic psychiatry at the University of British Columbia, largely concurred, saying the "majority of successful insanity defences are done when both the defence and Crown psychiatrists agree." In the Magnotta case, of course, they do not.

4. Flight to Europe

Another factor that could work against Magnotta's defence is that hours after slaying Lin, he purchased a plane ticket to Paris and flew there the next day.

It looks like the organized, concerted behaviour of someone trying to flee because they've done wrong, said retired B.C. Crown attorney Glenn Kelt, who prosecuted child killer Allan Schoenborn, a case where the not criminally responsible defence prevailed.  

"In a typical schizophrenic homicide, the guy's sitting there when the police show up," Kelt said. "They've got a delusional system of beliefs that is as true for them as anyone else's, so if they're justified in what they've done, why would they leave?"

O'Shaughnessy said he's seen multiple cases where someone suffering from psychosis hears voices, or is hounded by demons, commanding them to kill. "They don't flee and they don't try to cover things up. They realize, 'I've made a mistake. I've been duped or tricked.'"

In Magnotta's case, he also spent hours cleaning up his apartment after killing Lin, disposing of screwdrivers, rubber gloves, a hammer and scissors.

Jurors may be inclined to see it as the all too rational steps of someone who is trying to get away with murder.

5. Maverick juries

Ultimately, it's impossible to confidently predict which way the Magnotta jury might go. "Juries misunderstand mental disorders and have their own views," said Deanne Gaffar, a Vancouver lawyer who has handled many NCR cases, including the high-profile trial of Kimberley Noyes.

There's perhaps no better example than in the prosecution of B.C. woman Dorothy Mercredi for stabbing her neighbour to death in 2000. The Crown argued she was not criminally responsible because she suffered from schizophrenia. The defence agreed. So did expert psychiatrists for each side. And so did the judge, who told the jury a finding of NCR was preferred.

But despite all that, jurors found Mercredi guilty of manslaughter (the verdict was overturned on appeal).

In other words, no matter how strong the evidence one way or another, jurors sometimes decide what they want, based on their own gut feelings.

"Juries are a bit more realist," said lawyer Phil Rankin, who represented Mercredi. "When you sit next to a guy on a bus and he slits your head, they're just afraid of him. They don't want them to be out on the street."

And they're worried that's what will happen with a not criminally responsible verdict. Said forensic psychiatrist Bradford: "They've been brainwashed to think the person is going to walk out the door in five minutes."