A Canadian man accused of dismembering his Chinese lover and mailing the body parts to schools and political parties around the country has admitted to the killing in court, but his lawyer says he is not criminally responsible due to his mental health.

The trial against Luka Magnotta, 32, in connection with the murder of 33-year-old engineering student Lin Jun in May 2012, started on Monday in Montreal.

Magnotta faces five charges, including first-degree murder, committing an indignity to a body, publishing obscene material, criminally harassing Prime Minister Stephen Harper and other members of parliament, and mailing obscene and indecent material.

Standing behind a glass panel beside his lawyer, Magnotta responded "not guilty" to each of the five charges.

Luc Leclair said his client has been diagnosed with schizophrenia and is therefore not criminally responsible.

"A person is not responsible if he or she suffers from a mental disorder at the time of the act," he told the jury.

Leclair said his witnesses are likely to include Magnotta's father, Donald Newman, a diagnosed schizophrenic.

The judge said the jury will have to decide whether the acts were committed "with the required state of mind for each offence".

Crown Prosecutor Louis Bouthillier told the jury he will demonstrate that the crime was planned six months in advance and show Magnotta laid out those plans in an email to a London journalist who will testify during the trial.

“It is our position that this email makes it clear that Mr Magnotta was planning to kill a human being and that he was going to make a movie of that killing," he said.

In his opening remarks, Bouthiller warned the jury to expect "graphic" and "gruesome" evidence, including the video and photographs of Lin's dismembered body.

Severed foot

The jury selection for the trial took two weeks as the prosecutor and Magnotta's lawyer chose from about 1,600 candidates, aiming to find impartial jurors not influenced by the intense publicity surrounding the 2012 murder and manhunt.

The case gained extensive international attention after a package containing a severed foot was found at the headquarters of Canada's ruling Conservative Party in May 2012.

The same day, a hand was discovered at a postal facility, in a package addressed to the Liberal Party of Canada.

Days after the killing, the victim's torso was found in a suitcase by the rubbish outside Magnotta's apartment building in Montreal.

Magnotta fled Canada but was arrested in Berlin in June 2012, after an international manhunt.

Lin's father, Diran Lin, travelled from China to attend the trial.

The trial is expected to last six to eight weeks, with testimony from 60 witnesses.