CAMPBELLTON, N.B. -- After more than a week of testimony, the trial of a man whose African rock python escaped and killed two young New Brunswick boys came down to one question: Did his decision not to cap a ventilation pipe constitute a crime?

Both the Crown and defence presented their closing arguments Tuesday in the Court of Queen's Bench in Campbellton.

The defence said Jean-Claude Savoie didn't cover a ventilation pipe above his python's enclosure not because he was careless or reckless, but because he simply didn't believe the large snake could possibly fit through it.

Savoie pleaded not guilty to criminal negligence causing death after the python escaped an enclosure in his Campbellton apartment and killed four-year-old Noah Barthe and his six-year-old brother Connor in August 2013.

The python travelled through a ventilation duct and dropped into the living room where the boys slept. Savoie's own son, sleeping in another room, was unharmed.

A number of witnesses have said it was common to see the cover of the vent on the enclosure's floor.

Defence lawyer Leslie Matchim said Tuesday the snake did try to escape about a month or so before the boys were killed, but got stuck partway through the pipe, convincing Savoie and others that it could not escape that way.

"They were wrong, but not from a lack of caring," he said.

Matchim said Savoie didn't go out and buy the snake. The Canadian Wildlife Service asked him to take it after the snake was seized in Saint John, and Savoie was never given any money to care for the snake in the subsequent 11 years.

Savoie lived in the apartment with his three-year-old son.

"Would he put his own safety and that of his son at risk?" Matchim asked.

The boys had spent Aug. 4, 2013, petting animals and playing at a farm owned by Savoie's father before a sleepover in Savoie's apartment.

Matchim said the trip to the farm with the children showed Savoie was a good father and guardian and was not cavalier with their safety.

Matchim said the issue here is foreseeability.

"Does omission constitute criminal negligence?" he said.

He said Savoie didn't cover the ventilation pipe because he didn't think there was any chance the snake could exit through the ventilation pipe.

"There is no need to install a barrier if you've come to that conclusion in your mind," he said.

Matchim said there's no proof Savoie was being reckless.

"Accidents happen, but not everyone who causes an accident is guilty of criminal negligence causing death," he said.

He says if the jury finds reasonable doubt, they must find Savoie not guilty.

But Crown prosecutor Pierre Roussel said Savoie had a legal duty to care for Noah and Connor Barthe when they stayed in his apartment. He was the only adult there.

"Mr. Savoie obviously failed in that duty," Roussel said.

Roussel said snake experts Bob Johnson and Eugene Bessette both testified the first thing they would do after an attempted escape would be to block the opening.

"Mr. Savoie failed to do that," Roussel told the jury. "That shows wanton and reckless disregard for the safety of others."

Roussel said Savoie should have foreseen that his failure to take action could result in the snake escaping.

"By failing to take action that's when he became negligent," he said.

Earlier in the day, Bessette, a snake expert from Florida testified it would have been "common sense" to cover the ventilation pipe after an escape attempt.

Bessette was the only witness for the defence.

During cross-examination by Roussel, Bessette told the court he was impressed by photos of the snake's enclosure in Savoie's apartment, calling the locked door "very sufficient" security.

Roussel referred to earlier testimony about the snake's escape attempt through a ventilation pipe above the enclosure, and asked what Bessette would have done if there was such an escape attempt at his snake farm.

"I would have made an attempt to rectify the situation," Bessette said.

"You would have covered the opening?" Roussel asked. "You would cover the hole for the safety of the animal and the public?"

"That would be common sense," Bessette said.

Judge Fred Ferguson will instruct the jurors on the law and their duties Wednesday morning before they begin their deliberations.