Dr. Thomas Barth treated Magnotta for roughly one week after his arrest in Berlin on an international warrant after the slaying of Jun Lin in Montreal.
Crown prosecutor Louis Bouthillier questioned the defence witness Wednesday about whether he believed Magnotta's disorganized, chaotic ramblings were done deliberately to ensure there would be a record of his symptoms for an eventual trial.
Barth was adamant he had not been led astray.
"I strongly believe and I still believe that Mr. Magnotta was very ill at the time he was treated by me and my colleagues at the Berlin prison hospital," he told Magnotta's first-degree murder trial.
Magnotta, 32, has admitted to killing the Chinese engineering student, but has pleaded not guilty by way of mental disorder.
Bouthillier confronted Barth with elements of Magnotta's behaviour and previous medical records that seemed to contradict what the accused told the psychiatrist.
For example, Magnotta told Barth he'd left his anti-psychotic medication at the home of a German man he'd been staying with but Bouthillier noted Berlin police found nothing of the sort.
In another example, Magnotta told Barth he didn't drink much. But previous trial evidence revealed the accused had been drinking while partying at gay clubs in Berlin for a few days prior to his arrest.
Bouthillier also cited a Montreal hospital report from April 2014, roughly two months before Barth saw him.
In that document, Magnotta told doctors he drank up to six glasses of wine a day. It also stated that doctors determined he did not appear to suffer from psychosis or previously diagnosed bipolar disorder.
Barth said none of those findings are surprising or uncommon in schizophrenics. Patients are seemingly fine one minute and distressed the next, often hiding their symptoms.
"That is the typical picture I see when I deal with psychotic patients," Barth said. "It is the problem with treating schizophrenia patients — a little change in their lives can lead to a relapse."
Barth said the patient he observed appeared disorganized, confused and distressed.
Bouthillier suggested to Barth that Magnotta "wanted you to believe he was crazy — wanted the world to know that he was crazy."
The German psychiatrist testified he was also aware of malingering — a medical term used to describe the faking of mental illness. But he said he didn't believe this applied to Magnotta.
"Did you know Mr. Magnotta was an actor?" Bouthillier asked with his final question.
No, Barth replied.
On Tuesday, Barth told the trial that Magnotta rambled during their first session, offering bursts of information before quickly changing the subject.
But the German doctor said he had no reason to probe any further than he did in his initial exchanges. He was never able to gain access to Magnotta's health files before his patient was extradited to Canada.
Later on Wednesday, the trial heard from Dr. Renee Roy, Magnotta's treating psychiatrist.
Roy testified that Magnotta was hearing voices and was treated for auditory hallucinations linked to anxiety. Those symptoms were still present in April 2013 and manifested themselves again this past August during pre-trial hearings.
Roy said Magnotta told her he was hearing noises in the form of murmurs, "like he's got a cellphone in his head."
In May 2013, Roy noted in a report that Magnotta was hopeful about delivering his version of events at his eventual murder trial.
She said his ability to communicate improved as his medications stabilized.
Roy is due to be cross-examined Thursday.
Magnotta faces four charges in addition to the premeditated murder of Lin: criminally harassing Prime Minister Stephen Harper and other members of Parliament; mailing obscene and indecent material; committing an indignity to a body; and publishing obscene materials.
Follow @sidhartha_b on TwitterSuggest a correction