SAINT-JEROME, Que. -- A defence witness testified Thursday that Guy Turcotte's mental state the night he stabbed his two children to death prevented him from developing an intent to kill.

Dominique Bourget was back on the stand for a second day at the former doctor's first-degree murder trial in the February 2009 slayings of his two young children.

Bourget told the jury she believes the acts were the product of man whose brain was profoundly sick.

His brain was not working like a normal person's, Bourget said, adding that Turcotte was disconnected from reality.

"He was in a state of mental confusion and was out of touch with reality," she said. "He was thinking so much about dying, he was no longer thinking of anything else."

Turcotte, 43, has pleaded not guilty to two counts of first-degree murder in the slayings of Olivier, 5, and Anne-Sophie, 3.

He has admitted to causing their deaths but his lawyers are arguing he should be found not criminally responsible by way of mental disorder.

Bourget, a forensic psychiatrist with a specialty in domestic homicides, is crucial to that defence.

On Wednesday, she told the court that Turcotte was suffering from an adjustment disorder, exhibiting signs of anxiety and depression with obsessive-compulsive traits.

She also said Turcotte was in an acute suicidal crisis.

Turcotte told jurors at his trial last week that on Feb. 20, 2009, he had decided to end his life and began drinking windshield washer fluid -- which contains methanol. As he went about his plan, he decided to bring his children with him.

Bourget testified Thursday that Turcotte was not thinking of killing his children the night they died.

"For him, at that moment it's not to kill, it's to bring his children with him," she said.

She said this logic was clearly faulty and irrational.

"We understand that this way of thinking is highly abnormal and can be explained, in Mr. Turcotte's case, by the presence of psychiatric illness," she wrote in her July 2015 report.

She said a parent who is contemplating suicide doesn't think about killing, but rather about an "expanded suicide" because a good parent doesn't want to abandon their child and leave them behind.

His actions are all the more "absurd," she said, "because he's causing them to suffer (by killing them)" to spare them the suffering of finding their father dead.

Bourget testified at Turcotte's first trial in 2011 and saw him again in July 2015 to make a second report.

In his cross-examination, Crown prosecutor Rene Verret questioned whether Bourget had been too willing to believe everything Turcotte told her during her analysis.

He asked Bourget to explain why on the day of the killings Turcotte was able to go to work, call his mother and cancel two appointments if his brain was not working properly.

Bourget responded that Turcotte's brain wasn't working well but it could still make "certain connections."

Bourget's cross-examination will continue Friday.