MONTREAL - The former wife of a Quebec doctor who was found not criminally responsible for killing their two young children called for changes to the justice system on Saturday as she joined provincewide protests against the verdict.

Isabelle Gaston said she accepts the jury's decision on Guy Turcotte but wants stricter guidelines for when a not-criminally-responsible verdict can be rendered.

"The time has come that we should rethink the way it's evaluated," she said at a demonstration in Montreal, a month after the verdict was rendered on July 5.

It should be up to a team of independent psychiatrists and a judge, rather than the jury, to determine the mental state of the person on trial, Gaston said.

"The (question of) criminal responsibility is something too big, too important, too complicated to be in the hands of people that don't have the knowledge of psychiatry."

Turcotte, a former cardiologist, admitted to causing the deaths of his two children in 2009, but denied criminal intent.

The jury of seven women and four men had several possible verdicts from which to choose: first-degree murder, second-degree murder, manslaughter, or not criminally responsible for reason of mental illness. Acquittal was not an option.

Many protesters in Montreal said they were upset with the verdict and the justice system in general. Others expressed dismay at the possibility that Turcotte could soon be free.

On Aug. 12, he is due to appear before a mental health tribunal that will determine whether he is fit to be released or if he should be detained for another year.

The demonstration began early Saturday, and by noon dozens of stuffed animals, candles and photos of the two children had been placed on the Montreal courthouse steps.

Several people, including Gaston, wore T-shirts featuring a photo of her two children -- Anne Sophie, 3, and Olivier, 5 -- along with the words "Justice" and "Don't close your eyes, we can change things."

Others held up placards with slogans such as "Mental problems aren't a licence to kill" and "Injustice in Quebec.

Chantal Rondeau of Montreal brought her 10-year-old boy to the protest to show support for Gaston.

"I am a mother, and when the verdict came down, I was shocked," she said. "I was crying a lot."

Experts testifying at trial on his behalf said Turcotte was not aware of his actions the night he killed his children, just weeks after his marriage had ended.

Turcotte couldn't explain why he stabbed his two children a total of 46 times while they were lying in their beds.

He was suffering from depression and testified that he felt increasingly marginalized by Gaston's new boyfriend.

The Crown has announced it's appealing the verdict, saying it believes the judge erred in law in his instructions to the jury. It has also asked the Quebec Court of Appeal to hear the case.

After first hearing the verdict, Gaston said she wanted nothing more to do with the courts. But she has since offered her support for the Crown's appeal.

On Saturday, Gaston said she was encouraged by the turnout at the protest.

"I'm always sad but today I feel less alone," she told reporters.

"When you're a victim you feel that the system doesn't listen to you, so today the presence of (all these people) gives me a lot of energy."

A smaller protest was also held Saturday in Quebec City. Others were planned in a dozen more cities across the province.