03/22/2012 12:33 EDT | Updated 05/22/2012 05:12 EDT

Alberta boys' deaths 'shrouded in mystery'

Allyson McConnell's drowning of her two young sons is an "unspeakable tragedy … still shrouded in mystery," her lawyer argued at her murder trial Tuesday.

"You could never imagine a sadder case than this," Peter Royal said. "How could this fine woman do such a terrible thing?"

McConnell, on trial for second-degree murder, has testified she understands she drowned two-year-old Connor and 10-month-old Jayden, but insists she cannot remember doing so. Their bodies were found by their father, Curtis McConnell, in the water-filled bathtub of their Millet home, 40 kilometres south of Edmonton, on Feb. 1, 2010.

The defence has been trying to convince the judge that McConnell was so depressed and possible drugged, she could not form the intent to kill.

"It's hard to remain untouched by what has happened here," Royal told the court in Wetaskiwin, Alta.

The immediate response in the community was understandably one of horror followed by repugnance, he said. "But we must ensure justice is done," Royal said. "Ally was a loving, caring parent. We know she was devoted to her children."

McConnell, 33, and her husband were going through a difficult divorce and a bitter custody battle and was severely depressed, Royal said.

"A failing marriage and two energetic, beautiful sons," Royal said. "She felt alone, isolated, useless … just buried in a load of crap. We all know now she was suicidal."

But it's not clear when McConnell drowned the boys, he said.

The boys died between Friday night and Monday morning, he said, but whether they died before or after McConnell tried to kill herself with alcohol and sleeping pills "we don't know."

Earlier in the trial, Dr. Alberto Choy testified McConnell saw her sons as the only aspects of her life with any value. The psychiatrist said McConnell was suicidal and wanted to take her sons with her, not wanting to be separated from them even in death.

Royal concluded McConnell is guilty of manslaughter, not murder.

But Crown prosecutor Gordon Hatch took little time in arguing the judge's decision is clear.

"This was a prolonged and purposeful act that promotes only one conclusion: intent," he told Court of Queen's Bench Justice Michelle Crighton.

Crighton will render her decision on April 20.