Police stand outside the north Edmonton townhouse where the bodies of two boys were found on Dec. 20. (CBC)

In an exclusive interview with CBC News, an Alberta mother is speaking publicly for the first time about the day her two children were killed, allegedly by their father.

She is calling for a public inquiry into the deaths after having raised mental-health issues about the father months ago.

The two boys, aged six and three, were found dead in a north Edmonton townhouse on Dec. 20, 2010. Their father, Jason Cardinal, 31, was charged with two counts of first-degree murder.

The mother, who cannot be identified, said she was accompanied by a provincial family support worker on the afternoon of Dec. 19 to pick up her children.

The father had the boys for a weekend visit and the support worker was there to supervise the transfer between the parents because of an interim custody order.

The mother said she knocked on the door with the social worker and then later with a family member to try to retrieve her children. No one answered the door.

"And we kept going back every couple of hours," the mother said. Each time, no one answered.

"I was stuck. Nobody would respond. The cops wouldn't do anything," she said.

Edmonton police were called to the home by social services early that evening to check on the children's welfare. But there was no response, so they waited for a court order to enter the home.

Shortly after midnight last Dec. 20, officers found the boys' bodies, along with Cardinal, who had injuries that were not life-threatening.

"I was angry at them, and I told them, 'You can't do anything for me now,'" the mother said. "I tried. It doesn't matter anymore."

There are now questions about why the father was allowed unsupervised visits with the boys.

Ten months earlier, the Alberta Children and Youth Services took custody of the children over concerns about Cardinal's mental health — concerns the mother raised after he was allowed to have them overnight on weekends, unsupervised.

"He wasn't capable, and I know he wasn't and that's the very hard part …. My sons had to pay the ultimate price for the negligence."

With files from CBC's Trisha Estabrooks