Man found guilty of sex assaults against three women outside Calgary

CALGARY – A man was found guilty Tuesday of sexually assaulting three vulnerable women, and drugging one of them, at a rural home east of Calgary.

Richard Robert Mantha, 62, was convicted of six offences: two counts of sexual assault, choking while committing a sexual assault, administering a noxious substance, assault with a weapon, and uttering threats against a fourth woman.

Justice Judith Shriar dismissed charges relating to two other complainants.

Mantha, who initially faced 20 charges, was accused of attacking seven women between August 2019 and April 2023. Court heard most of the women worked in Calgary’s sex trade.

Charges involving the seventh complainant were earlier dismissed, because she died before the trial.

The judge, in reading the verdict for nearly two hours, said it was clear during the trial that the women did not mistakenly identify Mantha.

“All the complainants identify Mr. Mantha in the dock. The complainants’ interaction with the accused were neither fleeting glances nor brief encounters with a stranger,” Shriar said.

“The evidence of identity is overwhelming, and the court has no doubt that at all material times each of the complainants were interacting with the accused.”

However, Shriar said she wasn’t convinced on most of the drugging charges — administering a noxious substance to endanger life or cause bodily harm. She found Mantha guilty on the one lesser count of administering a noxious substance with the intent to aggrieve or annoy a person.

“An accused cannot be found guilty of administering a noxious substance … if the complainant voluntarily consumed it,” the judge said.

It has been more than two years since Mantha’s trial began in Calgary.

The trial, which started in January 2024, faced several lengthy delays because he fired previous lawyers and suffered a stroke.

A forensic psychiatrist assessed Mantha to determine how the stroke affected his cognitive capacity, and he was found fit to stand trial despite reduced verbal skills.

During closing arguments in December, Crown prosecutor Dominique Mathurin said Mantha supplied drugs to the women and, in every case, the women were unconscious or severely impaired.

Mantha’s lawyer, Justin Dean, urged the judge to look closely at the reliability and credibility of some of the witnesses, particularly given their heavy drug use. 

Shriar appeared to address that in her verdict.

“There is no hierarchy of witness credibility,” the judge said. “Determining credibility is an issue of fact. No witness is entitled to greater credibility because of who or what they are.”

Mantha is to be sentenced at a later date.

This report by The Canadian Press was first published April 7, 2026.