An Edmonton Court of Queen's Bench judge has found a former foster mother guilty of a lesser charge of manslaughter in the death of three-year-old boy in her care.

Lily Choy, 37, was on trial for second-degree murder.

The boy, who cannot be named under Alberta's Child, Youth and Family Enhancement Act, died of massive head trauma in January 2007 after he struck his head on a toilet bowl. 

Justice Donna Read said she has no doubt Choy repeatedly spanked the little boy so severely it left him covered with bruises on his head, arms, buttocks and back.

She also accepted the evidence of Julia Gee, a nanny who worked for Choy. Gee testified that Choy left the boy outside in the cold garage for two nights, clad only in a diaper.

The judge rejected Choy's testimony that the boy hit his head after jumping out of her arms.

"I did not find her evidence credible," she said. "I do not believe her version of events about what caused the boy's injury."

Since she was unsure beyond a reasonable doubt exactly how Choy hurt the boy, the judge could not convict her of second-degree murder.

The manslaughter conviction came as a surprise to Edmonton homicide Det. Bill Clark. 

"I fully expected we were looking at a second-degree murder conviction," he said. "I have to say I was very surprised right at the end when she dropped it to manslaughter. I just hope that we now see a sentence that fits the crime."

This is the second time Choy has been on trial. A jury convicted her of manslaughter in November 2008 and she was sentenced to three years in prison. Last year, the Alberta Court of Appeal overturned the conviction and ordered a new trial.

Choy was set free on bail and will be sentenced Oct. 17. She earlier spent two months and two days behind bars in a minimum security jail before a judge set her free on bail pending her appeal.