A father who killed his two young sons five years ago was removed from an Edmonton courtroom Monday after refusing to answer questions about their deaths at a fatality inquiry.

"This is about one person gaining from a tragedy," Jason Cardinal told the judge. "I'm not going to help."

The boys' mother, Andrea Badger, is suing the province over her sons' deaths.

Cardinal was testifying about his involvement with the child welfare system during the time the two boys, Caleb, 6, and Gabriel, 3, were removed from his care.

The boys were found dead on Dec. 19, 2010, in an Abbottsfield home, 10 hours after their mother and a family support worker went to pick them up following a unsupervised weekend visit with Cardinal.

Two years later, Cardinal pleaded guilty to two counts of first-degree murder.

A fatality inquiry looking at how to prevent similar deaths began Monday.

As Cardinal began his testimony, he expressed reluctance to answer questions, but remained in the witness box.

The court heard that Cardinal became the main parent of the boys when his common-law wife went to work at a camp outside Bonnyville, Alta., in late 2008.

Cardinal was living with the boys on the Goodfish Lake Reserve.

Accused of spanking sons

He said he did not remember when he moved to Edmonton, but it was soon afterwards that Child and Family Services first became involved with the family.

In May 2009, one of the boys got out the front door of the Abbotsfield home wearing only a diaper after Cardinal fell asleep.

In February 2010, Child and Family Services received a complaint that Cardinal was spanking the boys.

At the time, Cardinal admitted he had spanked the boys, but said he no longer did.

The boys were apprehended.

By the end of March that year, he was allowed supervised visits with the boys twice a week.

He told the court he was unhappy with how Child and Family Services treated him.

"My experience with all of those people is negative," he said.

After his kids were taken away, he lost his role as a functioning parent and started to decline, he told the court.

He acknowledged he has had various forms of mental illness since the age of nine, including bipolar disorder.

After he was advised to take steps to make himself a more effective parent, he took parenting courses in the summer of 2010.

Things began to unravel

He eventually earned the privilege of having the boys stay with him on weekends, but that's when things began to unravel.

Cardinal admitted to forging a doctor's signature to obtain drugs and later was caught shoplifting.

A doctor's report at the time diagnosed him with various conditions, including generalised anxiety disorder and sociopathic tendencies.

However, his access to the boys went unchanged.

The inquiry lawyer presented Cardinal with a letter that he wrote dated Dec 5, 2010, that detailed a plan to kill the boys and himself.

Cardinal said he couldn't remember writing the letter and did not believe the date was accurate.

He said he was heavily medicated during that "last month" and doesn't recall any dates.

Two weeks later, the boys were found dead.

After the inquiry broke for lunch, Cardinal refused to answer any more questions.

The inquiry moved on to the boys' mother.

Badger said she felt Child and Family Services was not entirely open with her and did not listen to her concerns.

Asked if the province could have done anything to prevent the deaths, she said workers should have taken Cardinal's mental health into consideration.

"It was deteriorating and he was being pushed like a rat in a corner," she said. "He was going to do something. Hurt himself or others."

She said she did not agree with the unsupervised visits, but felt there was nothing she could do.

Outside of court, Badger was asked what it was like watching Cardinal testify.

"He hasn't changed," she said.

The inquiry is scheduled to last the rest of the week.