BARRIE, Ont. - A jury deciding the fate of a mother who drowned her young daughters must decide whether she was so gripped by mental illness that she didn't know it was wrong, or whether her actions were driven by pure vindictiveness in the midst of a custody battle.

Elaine Campione, 35, is charged with two counts of first-degree murder in the deaths of Serena, 3, and Sophia, 19 months.

The jury retired Wednesday without a verdict after their first full day of deliberations following a seven-week trial. Deliberations were to resume Thursday.

The defence concedes Campione drowned her children, but is urging the jury to find her not criminally responsible by reason of mental disorder.

Lawyer Mary Cremer argued it was a "recipe for disaster" when a mentally ill single mother was released from a psychiatric ward after a suicide attempt with little more than a prescription and sent home alone to care for her daughters.

Campione believed she was being followed by people trying to kill her and take the girls away in the months leading up to the killings, Cremer had told the jury. She said her client's bizarre behaviour included refusing to let one of her daughters touch anything red and claiming she saw aliens.

She believed the girls would only be safe in heaven, Cremer said.

The Crown alleges Campione killed the girls and tried to kill herself just days before a family court date because she didn't want her abusive ex-husband to get custody. She had just learned medical records detailing her extensive psychiatric history would be raised.

Crown attorney Enno Meijers reminded the jury that Campione had previously told her sister that if she couldn't have Serena and Sophia, nobody could. Court heard evidence that drowning would take two minutes or more under water, Meijers said, and urged the jury to think about the determination it would take to hold a child under water for two minutes -- then to do it again.

The six-woman, six-man jury must decide if Campione is guilty of first-degree murder, second-degree murder or manslaughter, or if she is not criminally responsible by reason of mental disorder.

Minutes after Campione calmly called police on Oct. 4, 2006, saying her children were dead, officers found the girls in their mother's bed, dressed in their pyjamas, holding hands and lying with a photo album and a rosary.

A videotape was found in the room on which Campione addressed the camera, speaking as if she and her daughters were dead.

"Leo, there are you happy?" she says. "Everything's gone ... The idea that you could actually have my children -- God believes me and God's taking care of them now."

She goes on to spew vitriol about her ex-husband, calling him a "hideous monster" and "the devil."

"I want you to know how much I hate you," Campione says on the video. "You couldn't leave us alone. You wanted to win and you won ... Are you happy? ... You beat your wife to death and your children and don't you ever, ever, ever forget it."