He sobbed on the witness stand Tuesday as he recalled how he pulled 2-1/2-year-old Connor and 10-month-old Jayden from the tub and placed them on the floor of the family's home in Millet, Alta., south of Edmonton.
"They were so cold and stiff," said McConnell, his face red and wet with tears.
"She just left them in there to rot. I had to look away. I didn't want to see their dead faces."
He said he frantically ran to get a neighbour to come and look in the bathroom, just in case he had imagined the whole thing.
Allyson McConnell is on trial on two counts of second-degree murder. She admits to drowning the children in February 2010 but has pleaded not guilty to the charges.
The central issue at trial is her state of mind when she did it. The same day she killed her children, she tried to commit suicide by jumping off an Edmonton overpass.
As her former husband testified, the 33-year-old woman sat in the prisoner's box and dabbed briefly at her eyes while she stared at her lap.
Back in 2010, the couple were in the middle of a bitter divorce and fighting over custody of their boys. Allyson McConnell, who is from Australia, wanted to move back with the children.
Curtis McConnell testified that at first he couldn't understand why his wife would kill their boys. He talked with police about the possibility that she was depressed or had postpartum depression.
But he said he later came to believe she killed the children because she hated him — and that she orchestrated the event so he would find their bodies.
He said the day the boys were killed, the home was locked and he was the only one who had a key. His estranged wife also left her wedding ring on top of the toilet next to the tub.
Curtis McConnell recently filed a lawsuit against his wife asking for damages for the children's deaths. The suit claims the boys' deaths were "flagrant and outrageous and intended to cause (Curtis McConnell) serious psychiatric injury."
"I would say she would do it to hurt me," he testified. "Only Allyson knows for sure."
The couple recently finalized their divorce. But in 2005 their relationship had started out as a whirlwind romance. The boys' father testified that he was working at a ski resort hotel near Kamloops, B.C., when his future wife moved in next door. She was on a working holiday, travelling around the world and had just finished a stint in South America.
They started dating a few weeks later and travelled to Australia together the following year. In 2007, after discovering she was pregnant with their first child, they got married, then moved to Millet to be close to his family.
Curtis McConnell worked at the Home Hardware store in nearby Wetaskiwin and his wife did accounting work for an oilfield company.
He said they were happy until they returned from a family trip to Australia in the spring of 2009, a few months after their second boy was born. He said his wife became withdrawn and he later discovered she was making plans to move back home with the children.
He filed for divorce and kept the children's passports for safekeeping. A court order later ruled the children had to remain in Alberta until custody could be decided.
He had moved out of the house and their relationship was strained. But McConnell said his wife was a good mother. He thought she looked tired but showed no signs that she would try to hurt herself or their children.
On Feb. 1, 2010, he was getting ready to start an afternoon shift at work when he got a phone call from police telling him his wife had fallen off a bridge in Edmonton.
"Where are the kids?" he asked.
Police told him they were unable to get information out of his wife, who was being treated in hospital for broken bones.
He testified that police wanted him to come to be with her, but he wanted to go check to see if his children were at home. As he was driving, police phoned back and told him not to worry. They had spoken with his wife and she said a friend was looking after them at their house.
But when he got there, no one was home. He knocked on the door, then let himself in with his key. The TV was blasting. He looked for the phone so he could call friends to see if they had the boys.
He found the phone in the master bedroom and noticed that a blow dryer and hair iron were lying in a tub full of water in the ensuite bath.
He panicked and screamed. If his wife had tried to kill herself, he suspected she may have harmed their children.
He said he ran to Connor's empty bedroom, then to Jayden's room and looked in his crib. He saw the bathroom door across the hall was closed. That was unusual. They kept it open because Connor was potty training.
The door was locked, so he grabbed a knife to pop it open.
"It smelled like dead bodies," he sobbed. "I just dropped to my knees."
An agreed statement of facts submitted in court said after Allyson McConnell drowned the children, she drove to Edmonton and parked outside a Toys R Us store. She walked to a hotel and ordered lunch but became upset and left.
She went to a bridge over Whitemud Drive, one of the city's main freeways, jumped over the railing and fell onto the pavement below. She was treated in hospital for broken legs, pelvis and collarbone.
Investigators found several searches on Allyson's computer relating to suicide and drowning on its hard drive.
"How long does it take to drown?" was one search made a few weeks before the boys were killed.
"How long does it take to die from strangulation?" was another search made the morning they died.
Officers also found a rope tied to a joist in the basement. A chair was sitting underneath.
Court heard Monday that Allyson McConnell had started giving away the children's belongings a few days before the killings.
A judge has already found her fit to stand trial but she remains a mental health patient at Alberta Hospital. Defence lawyer Peter Royal said his client is severely depressed and on around-the-clock suicide watch.