The legal counsel of Luka Rocco Magnotta was widely expected to request a psychiatric evaluation of their client on Thursday as his initial defence lawyer suggested the possibility earlier this week.

Although his defence team ultimately decided against, his lawyers could still build their case on Magnotta's state of mind during the crimes he's alleged to have committed.

It's also possible that Magnotta, who has pleaded not guilty to first-degree murder, could be found fit to stand trial, only to have his defence successfully argue he is not-criminally responsible. (The case of Guy Turcotte, the Quebec cardiologist who stabbed his two children to death, is a recent example.)

However, in Canadian law, the standard for an accused to meet the threshold of not criminally responsible can be difficult, according to Norman Boxall, president of the Criminal Lawyers Association.

“It’s a fairly high standard to meet. You can have a significant mental illness and not meet that standard," Boxall told CBC News.

Under Section 16 of Canada's Criminal Code, a person is deemed to be not criminally responsible (the term 'insane' having been scrapped) if the crime was committed while "suffering from a mental disorder that rendered the person incapable of appreciating the nature and quality of the act or omission or of knowing that it was wrong."

"That could be knowing it was legally wrong or knowing that it was morally wrong," Boxall said.

Boxall, who wouldn't comment on the Magnotta case specifically, said the court presumes that those accused do not suffer from a mental disorder so as to be exempt from criminal responsibility,

That means that accused individuals are presumed sane and the onus is put on the defence to establish, on the balance of probabilities, that the person could not appreciate what they did was wrong.

As well, having committed what is considered a heinous act and/or having a mental disorder doesn't mean a suspect is automatically assumed not criminally responsible.

Magnotta is accused of killing and dismembering Chinese student Jun Lin and mailing his body parts to different places including the Ottawa offices of the Conservative Party of Canada, the Liberal Party of Canada and two Vancouver schools. He is also accused of posting a video of the events on the internet.

"Just doing horrendous things doesn’t mean you fit that test and just having a mental disorder doesn’t mean you fit that test. Many many offenders have mental disorders and maybe many persons wouldn’t have done things but for their mental disorder, but that’s not enough. The mental disorder has to be of a specific kind," Boxall said.

“It’s not enough just to say they did it because they had a mental disorder. That’s not enough. It has to be a mental disorder of such severity that they could not appreciate the nature and quality of the act or did not know it was wrong in either the moral or legal sense.”

The starting point of such a defence would be to have a psychiatrist examine the accused to determine whether the suspect has a mental disorder, the extent of that order and if it's of sufficient severity that it could meet either of those prerequisites.

There would also be an extensive investigation into the person's background as prior psychiatric history would be looked into, as well as actions before and after the crime. Most important would be talking to people who interacted with the accused over a period of time, Boxall said.

Canadian high-profile cases in which the accused was found not criminally responsible include Turcotte; Vince Li, who beheaded a fellow passenger aboard a Greyhound bus in Manitoba nearly four years ago and Jeffrey Arenburg, who shot and killed Ottawa sportscaster Brian Smith in 1995.

Boxall said it's possible to be in a state of so-called temporary insanity or not criminally responsible for a short period of time but it's rare and extremely difficult to argue.

"One would normally expect to see a progression of illness that could show this person had this mental disorder and of such severity."

"What’s helpful to a defence is if you can establish actions preceding [the crime] and post that shows the person is not capable of appreciating the nature and quality of acts or not knowing that it was wrong.”

Yet some lawyers may be wary of raising the NCR defence, knowing that juries may treat it with skepticism.

“I think there are studies of jury reactions to the insanity defence and I think it’s recognized there’s a fair bit of skepticism in the general public to the defence which can make it difficult to raise. Particularly if the facts are not such that the average member of the public thinks is crazy.”