A jury has found Guy Turcotte, the Quebec cardiologist who admitted he stabbed his two children to death, not criminally responsible because of a mental disorder.

The judge had instructed jurors that acquittal was not an option, as Turcotte admitted he stabbed his children, Anne-Sophie, 3, and Olivier, 5, in February 2009, in a rented home north of Montreal.

The 39-year-old physician was charged with first-degree murder, but always denied intent, and the defence focused on his state of mind at the time of the killings.

Guy Turcotte said he didn't know what he was doing when he killed his children. (CBC)The jury had to decide on one of four scenarios: first-degree murder, second-degree murder, manslaughter or not criminally responsible by reason of mental illness.

It reached a decision Tuesday, on what would have been the jury's sixth full day of deliberations.

The slain children's mother, Isabelle Gaston, admitted to being astounded by the outcome, despite having prepared herself for all scenarios.

"With this verdict, my path will really not be easy," Gaston told reporters at the Saint-Jérôme, Que., courtroom. "I'm in shock."

Gaston, who was separated from Turcotte when their children were killed, said society can still be proud of its justice system.

"Even if it had been first-degree murder I could not have been satisfied because it would not have brought back my children in this life," she said.

Gaston doesn't want an appeal and said she won't testify again.

"For me, and I speak for myself alone, it's over," said the emergency room physician. "I will never return to a trial."

Defence hinged on mental state

During the 10-week trial, Turcotte's lawyer Pierre Poupart argued that his client was suffering from mental difficulties that stemmed from his troubled marriage, and was not aware of what he was doing.

The Crown argued Turcotte had planned to murder his children, suggesting he was angry with his estranged wife for cheating on him, and wanted to get back at her by killing them.

Turcotte's lawyers argued that the cardiologist loved his children but was unable to cope with the breakup of his marriage and his wife's affair.

Feeling increasingly marginalized, he had sunk into a deep depression in the days leading up to his children's deaths.

The killings occurred just one month after the couple had split, during a weekend that Turcotte was caring for the children while Gaston was away on a skiing trip.

Olivier and Anne-Sophie were stabbed to death in 2009. (CBC)Turcotte testified that he only remembered bits and pieces of the evening he stabbed his children.

He said he planned to end his own life on the night of Feb. 20, 2009 after reading emails between his wife and her new lover, the couple's personal trainer Martin Huot.

Turcotte started drinking windshield washer fluid to that end, but decided at some point that he didn't want his children to wake up the following morning and find their father dead.

He told the court he decided to take the children with him.

Public outrage at verdict

The trial garnered unprecedented media attention, with members of the public lining up for hours every day for a seat in the courtroom.

Turcotte with his son Olivier. (CBC)Thirty-nine witnesses testified, including Turcotte, his parents, Gaston and numerous mental health experts.

News of the verdict spread like wildfire on the internet, with hundreds of people turning to Twitter and other social media to discuss the outcome.

Several major Quebec television personalities even weighed in to express their own personal disgust.

"Very, very, very disappointing verdict. Criminally not responsible! I don't believe it," wrote Guy A. Lepage, host of the popular television talk show Tout le monde en parle, on his own Twitter account.

Another prominent Quebec TV personality, Julie Snyder, wrote that she was crying while thinking of the verdict: "I'm astonished," she added.

Veteran lawyer and former Quebec crown prosecutor Robert La Haye said the public's emotional response is not surprising, but it's important to remember that juries are not supposed to be populist.

He said juries render justice based on evidence.

"They weighed the evidence, dissected it and decided at the end of the day, and concluded reasonably and without emotion," La Haye said.

Turcotte faces round of psychiatric tests

Crown attorney Claudia Carbonneau said she would study the case before deciding whether to appeal.

Turcotte with his daughter Anne-Sophie. (CBC)"At this point, after a long trial, our thoughts are with Anne-Sophie and Olivier, and the family of Anne-Sophie and Olivier," she said.

The children's tearful mother asked outside the courtroom to be left alone so that she could have her privacy again.

Gaston told reporters she hopes a place after life exists where she can see her children again. "I'd like a sign that they're all right, that they're happy," she said, in tears.

Turcotte's future is up to a psychiatric review committee that will assess his state of mind and his risk to public safety.

He will undergo a series of psychiatric evaluations at the Pinel Institute in Montreal before the committee decides whether he needs to remain in custody.

With files from The Canadian Press