CAMPBELLTON, N.B. -- A New Brunswick courtroom was gripped Wednesday by the testimony of a grieving mother whose two boys were killed by a python weeks after the owner was warned the snake's possible escape route needed to be better secured.

Jean-Claude Savoie is on trial on a charge of criminal negligence causing death. His 45-kilogram African rock python escaped an enclosure within his Campbellton apartment in August 2013 and killed Noah Barthe, 4, and Connor Barthe, 6, while they were having a sleepover.

It's believed the snake travelled through a ventilation duct.

Savoie, who now lives near Montreal, owned the Reptile Ocean pet store below his apartment at the time. He wept Wednesday as the boys' mother, Mandy Trecartin, talked about her sons.

She said she dropped them off for a sleepover that night certain they were in good hands.

"I felt they would be as safe with him as they would be with me," Trecartin testified.

Trecartin says they lived behind Savoie's apartment, and her sons were best friends with Savoie's son. She says Savoie was a good friend, although she hasn't seen him since Aug. 4, 2013.

They had spent that day with the boys at a farm owned by Savoie's father, where the boys played with a lot of animals.

That evening, she and her boyfriend dropped the kids at Savoie's apartment for a sleepover, something they did often.

At 6:49 the next morning, she heard pounding on her door, and heard Savoie saying: "Oh my God, your two kids are dead."

She said her boyfriend went next door with Savoie, and when he came back he told her: "It's true. It's a (expletive) nightmare but it's true."

One of the first officers to arrive at the scene said he was surprised such a large snake could move so quickly. But RCMP Const. Eric Maillet said Savoie was able to recapture the python.

"The snake coiled around his arm," Maillet said.

Savoie put the snake in its enclosure, where it could be seen through a large floor to ceiling window, he said.

"The snake started hissing at us and lunging and hitting the window with its face."

The python appeared to be trying to escape its enclosure again, said Maillet, who was concerned the snake wanted to feed and was trying to get back to the living room where the bodies of the boys were.

"It was going straight up in the air towards the vent opening," he said.

Maillet said he was quite surprised how the snake was able to stand straight up -- almost reaching the vent opening.

"I didn't expect such a large reptile to be able to do that."

He said the snake was put in a garbage bin and removed from the building.

Later Wednesday, another witness told the jury that the python had previously escaped its enclosure.

Ocean Eagles, a volunteer at Jean-Claude Savoie's reptile store, said the snake had escaped about two-and-a-half weeks earlier through a ventilation duct. She later said it could have been a month-and-a-half earlier, but she was confused on dates.

"(Savoie) told me he was sitting down in his living room and he looked up and the snake was halfway out," Eagles testified.

Eagles said she placed a cover over the ventilation duct, but warned Savoie it needed to be screwed on. She said she often cared for the "dangerous" snake and fed it rabbits, but was very cautious.

"I knew what the snake was capable of. It can overtake any man," she said.

Under cross-examination by defence lawyer Leslie Matchim, Eagles said the snake appeared about 2 inches larger in diameter than the duct, and she never thought it could escape through it.

"I would never think so when you look at the size of the snake. It would never cross my mind," she said.

Eagles said her children had stayed at Savoie's apartment before and she would not have an issue with them staying there, even after the first escape attempt by the python.

"I still can't think it could fit out that pipe, but it did," she said.

Judge Fred Ferguson had a few final questions for Eagles following her testimony, and asked her to look at a particular picture showing the ventilation duct. However, while flipping to that picture, Eagles burst into tears.

She sobbed and said "Oh my God," stating she had seen a picture of the dead boys.