An Ontario mother says her "nightmare is finally over" after Crown prosecutors withdrew a second-degree murder charge Tuesday and a judge acknowledged the damage that a disgraced pathologist's testimony had done to her life.

Tammy Marquardt was previously tried and convicted in the death of her son, Kenneth Wynne, who was only two years old when he died in 1993.

But as the years went by, it became clear that the unreliable testimony of disgraced pathologist Dr. Charles Smith had helped put Marquardt behind bars in what the Ontario Court of Appeal would later describe as a miscarriage of justice.

After Justice Michael Brown agreed to remove the charge against Marquardt on Tuesday, he told her that he wished wished to offer his "deepest expression of regret" about what she had been through.

Brown said it was tragic that it took so long to discover the "flawed pathology" that Smith once offered in court during Marquardt's own trial and others.

Outside court, Marquardt said her son could now rest in peace, now that her conviction has been overturned and the second-degree murder charge thrown out.

"My nightmare is finally over. The one thing that never should have happened has ended," she told reporters Tuesday.

At Marquardt's 1995 trial, Smith, who was then a respected pathologist, testified that the Ontario woman had either strangled or suffocated her young son.

Other experts have since said it was not possible to determine the cause of the boy's death, though Marquardt's lawyer previously argued her son was epileptic and could have died from a seizure.

The Ontario Court of Appeal quashed Marquardt's conviction earlier this year and a new trial was ordered.

But the Crown said Tuesday that it would not proceed with a new trial because of the flawed evidence from Smith and the fact that too much time has passed.

Marquardt's lawyer, James Lockyer, indicated to reporters Tuesday that his client intends to seek compensation from the province for what has happened to her since her son's death.

Lockyer has also represented William Mullins-Johnson, a Sault Ste. Marie, Ont., man who spent 12 years in prison after being wrongfully convicted of killing his young niece.

Like Marquardt, Mullins-Johnson was convicted in a 1994 trial in which Smith's testimony was a key factor.

In Mullins-Johnson's trial, Smith testified that his niece had been sodomized and asphyxiated. In actual fact, she died of natural causes.

In 2007, Mullins-Johnson was acquitted and last fall he was awarded $4.25 million in compensation from the Ontario government.

With files from The Canadian Press and a report from CTV Toronto's Tamara Cherry