Jacob Forman killed his wife with a sledghammer, then murdered his two daughters by choking them, according to details emerging from his sentencing hearing.

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Jacob Forman killed his wife by hitting her with a sledgehammer and then he strangled his two young daughters after taking them to church, court heard Monday.

Forman murdered his wife, Clara, during an argument about his drinking. Her last words, uttered between the first and second of three deadly blows, were "What are you doing?".

After killing his wife in the master bedroom of the family's Rutland home on Dec. 17, 2017, he was asked by the girls why their mother had been screaming. He told them she'd seen a spider.

Forman then shovelled the walk with his girls and took them to church, where he stayed behind after the service to help put away chairs. After returning home, he killed the children.

"He said (during a confession to police), he thought it would be better for them to go home to heaven than to grow up in a world where daddy had killed mommy," Crown prosecutor Murray Kaay said.

After telling the girls to put on their pyjamas and letting them watch Netflix for awhile, Forman told his daughters he wanted to "play a game" with them, Kaay said.

First, he took eight-year-old Yesenia to her bedroom. "Mr. Forman choked her from behind and she passed out right away," Kaay said. "He continued to choke her until her heart stopped."

Forman also used a child's toy, a horse head on a stick, to apply pressure to Yesenia's throat.

After murdering Yesenia, Forman killed seven-year-old Karina the same way, Kaay said.

Forman, who owned a .22 calibre rifle, then spent several hours contemplating suicide, but decided against it. He moved the bodies to the garage, wrapping Clara in a sleeping bag and putting Yesenia and Karina into two Rubbermaid containers.

Forman went to work as usual the next day, and bought cleaning supplies on the way home to try remove the bloodstains from the master bedroom.

Concerned when Clara didn't show up for work on Dec. 19, friends twice called the Forman's residence. On the first call, Forman said his wife wasn't feeling well. The second time, he said Clara had left him and taken the children.

The friend called police, who went to the Forman's home. Forman initially denied them entry, repeating the lie that Clara had left him. Suspicious, police soon returned and searched the home, finding the bodies in the garage.

Forman was charged with the first-degree murder of his two children, and the second-degree murder of his wife.

He originally pleaded not guilty when the trial began last week, apparently believing his self-described acute alcoholism would offer him a defence. But he changed his plea to guilty on all three charges just three days after the trial began.

The Crown is seeking life sentences with no parole eligibility for 35 years; 25 years for the murder of the girls, and a concurrent 10 years for the murder of Clara.

In murdering his own children, Forman demonstrated the "most egregious breach of trust imaginable", Kaay told Judge Allan Betton. "Mr. Forman killed his daughters in their own bedroom, which should be a place of safety," Kaay said.

Forman's assertion that he killed his wife in a fit of anger, and then murdered his children because he didn't want them to grow up knowing he was a murderer, "can only be described as narcissistic and selfish to a degree which defies comprehension", Kaay said. "He killed his children in a callous, cowardly manner."

Consecutive sentences for multiple killings are rare, but Kaay said they were warranted in this case because Forman's murder of his children hours after he killed his wife constituted "distinct acts", Kaay said.The girls' deaths, Kaay said, were separate from their mother's murder in terms of their time, mode, and motivation.

Defence lawyer Raymond Dieno is arguing for a sentence of 25 years before parole eligibility. He argued the killings were related to Forman suffering from the "terrible effects" of alcohol withdrawal.

"This person still doesn't really understand how he could possibly have done this," Dieno said.

Forman had no criminal record and the children "were not brutalized" before their deaths, Dieno said. "He (Forman) is not Clifford Olson; he's not a monster," Dieno said.

While the Crown said Clara's murder and the killing of the children were separate events, and thus deserving of consecutive sentences, Dieno opposed that characterization.

"This was one incident over time," Dieno said. "They are inextricably linked events."

After the defence submission, Betton indicated he would likely be able to deliver a sentence when the hearing resumes at 3:30 p.m.