Isabelle Gaston said she is hopeful that the retrial of her ex-husband, former Quebec cardiologist Guy Turcotte, will finally result in justice for her two slain children.

Guy Turcotte was found not criminally responsible in July 2011 in the deaths of his two children.

The Supreme Court of Canada on Thursday morning denied Turcotte's request to have a Quebec court decision ordering a new trial overturned.

Turcotte will stand trial again for the 2009 slayings of his two children after previously being found not criminally responsible because of a mental disorder.

Olivier, 5, and Anne-Sophie, 3, were stabbed to death in Turcotte’s home in Piedmont, Que., about 60 kilometres northwest of Montreal.

Though he admitted to killing his children, Turcotte was found not criminally responsible for reason of mental disorder by a jury and was committed to Montreal psychiatric hospital the Pinel Institute.

He was released 18 months later.

“I’m under the impression that my children did not have a fair and just trial,” Gaston told CBC News shortly after the Supreme Court ruling.

"We need to believe… that there could be justice for Olivier and Anne-Sophie," she continued.

Turcotte and Crown appeal judgments

In September 2013, the Crown appealed the 2011 jury decision, asking for it to be annulled and for a new trial to be ordered.

The prosecutor argued that the judge in the first trial should not have given the jury the option of finding Turcotte not criminally responsible.

Olivier and Anne-Sophie Turcotte were killed in 2009 by their father, Guy Turcotte.

The Quebec Court of Appeal agreed, and ruled in November that Turcotte would stand trial again on two counts of first-degree murder.

Turcotte turned himself in to police shortly after the ruling and has been detained at the Pinel Institute since his arrest.

At the time of the new trial order, Turcotte’s ex-wife, Isabelle Gaston, said, “A part of me is happy — we can’t help but rejoice [at] this news. But at the same time, a part of me is sad. I have the impression that I [will] have to live all those uncertainties, that distress and hopelessness that I experienced with the [not-criminally-responsible] verdict on July 5. But for me, it’s a first step in fixing a judicial mistake that is appalling.”

Gaston testified at a parliamentary committee in June 2013 to reform Bill C-54, or the not criminally responsible reform act. A transcript of her testimony can be read here.

She also spoke of the problem with expert witnesses at trials.

At Turcotte's original trial, medical experts testified the man had experienced mental problems as a result of his separation from Gaston.

Since Turcotte's original not-criminally-responsible verdict, Gaston has been actively campaigning to change the way expert testimony is currently used in criminal cases.

Last month, the Quebec Association of Psychiatrists issued recommendations relating to how expert witnesses are selected and used in court proceedings.

Among its recommendations, the association said it should be the judge and not the lawyers for the prosecution or defence who choose which experts will testify in court.