Dr. Gilles Chamberland concluded the main part of his testimony and gave the jury his conclusion on his fifth day on the stand.
Magnotta is charged with first-degree murder in Lin's slaying in May 2012. He has admitted to committing the acts but has pleaded not guilty by way of mental disorder.
In cross-examining Chamberland, defence lawyer Luc Leclair suggested the psychiatrist's opinions on the case were established even before Magnotta's arrest in Europe.
In media interviews in May and June of 2012, Chamberland described Magnotta as methodical, organized and showing no sign of mental illness. The psychiatrist, who never actually met with the accused, stood by those comments Tuesday, saying they were based on information available at the time.
His opinions haven't changed after viewing the expert reports prepared for the defence.
Two forensic psychiatrists have testified they believe Magnotta, now 32, was psychotic, had been untreated for schizophrenia for at least two years and was unable to tell right from wrong when he killed Lin.
Chamberland has raised doubts about Magnotta's schizophrenia diagnosis in the early 2000s but said even if it's taken as truth, there's nothing to indicate mental illness had severed his link to reality the night of the killing.
The Crown argues the crime was planned and deliberate.
Chamberland said the best way to evaluate the intensity of an illness is to see how ths symptoms manifest themselves.
"In the case of Mr. Magnotta, the information we have before and after the event indicate to me that he understood what he was doing was wrong," he said.
"Even if we admit the illness, there's nothing in there to tell me he didn't know it was wrong."
Chamberland said Magnotta's general medical history doesn't suggest schizophrenia hindered him over the years.
"The schizophrenia, if it's there, doesn't seem to have had a big impact on his life."
Leclair blasted Chamberland's report, accusing him of "cherry-picking" details and of ignoring important aspects of Magnotta's medical files. The defence lawyer made numerous references to schizophrenia in the accused's history.
Chamberland admitted he didn't read the documents in full, but wasn't expected to as a rebuttal witness.
He continued to stick to his theory that Magnotta's past psychotic episodes were more likely attributable to drug use than to a mental illness and that personality disorders more likely explained his behaviour.
"We know your theory, you've made it clear many times in the media in 2012," Leclair said.
Chamberland's earlier testimony on Tuesday touched on several issues, including what he said are numerous parallels between Magnotta's case and the movie "Basic Instinct."
He called the similarities "fundamental" to the case. Lines from the movie are quoted in a letter by Magnotta suggesting six months before Lin's death that he would kill a human — an escalation from online videos he posted showing cats being killed.
"You see, killing is different then smoking...with smoking you can actually quit," Magnotta wrote.
Scenes from the video of Lin's dismemberment are staged in a similar fashion to some in the film, while there are links between names from the movie and some used by Magnotta.
In particular, Chamberland said the ice-pick theme is of concern as it's predominant throughout the movie and in Lin's slaying, where a silver-painted screwdriver was used. The film of Lin's dismemberment was entitled "One Lunatic, One Ice Pick."
"When we look at it all in hindsight, it's troubling," Chamberland testified.
The psychiatrist also suggested that someone suffering from schizophrenia would not have gone to such lengths as disposing of Lin's head in a Montreal park across town from his one-bedroom unit.
He said it's an example of behaviour that isn't consistent with someone suffering from psychosis or stress but rather with the attention-seeking personality disorder he believes afflicts Magnotta.
Chamberland also discussed watching a 2008 interview Magnotta did for a reality television show about cosmetic surgery.
Simply showing up for such an interview is uncharacteristic of someone with an illness, the psychiatrist noted.
The trial continues Wednesday.
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