The python that killed two young boys in Campbellton, N.B., escaped because of human error involving a missing fan in its enclosure, according to a former employee of the Reptile Ocean pet store.

"It was a flaw, it was actually a flaw," said Tim Thomas, referring to the large glass enclosure that went all the way up to the ceiling.

He revealed the information when he spoke last Friday to Urban Jungles Radio Network, a web-based radio program about reptiles.

"It's a ventilation fan that's in the ceiling, OK?" said Thomas. "Now, I'm not sure if it was me that took that fan out, because it had burnt out … or maybe somebody had taken the fan out and forgot to cover it up, replace it or what.

"But I mean, nobody would ever …. This is, like, a one-in-a-million-shot deal that this would actually happen, and it did. It did. Unfortunately, it did."

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Noah Barthe, left, and Connor Barthe pose in this undated photo posted on the Facebook page of Mandy Trecartin. (Facebook/Canadian Press)

Noah Barthe, 4, and his brother Connor, 6, were killed by an African rock python in an apartment above Reptile Ocean during a sleepover with the son of the shop's owner. The brothers' bodies were discovered on Aug. 5.

A preliminary autopsy found they died of asphyxiation.

Officials have said they believe the python, which was 4.3 metres long and weighed about 45 kilograms, made its way through the top of its enclosure and into a ventilation system before falling through the ceiling and into the living room of the apartment.

A criminal investigation continues.

'Heart of the matter'

A lawyer for Jean-Claude Savoie, the owner of Reptile Ocean, said the fan removal goes "to the heart of the matter," but declined any further comment.

"I wouldn't want to go down that road with you," said Leslie Matchim.

African rock pythons are illegal in New Brunswick.

Thomas told CBC News he worked for Reptile Ocean for 13 years and handled the python in question many times. He described the python as "vicious."

He said a green anaconda — also a banned species in the province — had previously been kept in the same enclosure.

"She was in there for two,  three years," said Thomas. "She never got through that, she never thought about it. It just so happened that the African rock did find it and did manage to do what she did."

The other enclosures at Reptile Ocean were well-secured with two locks — a slide lock and a master lock and key, he added.

Bry Loyst, from Peterborough's Indian River Reptile Zoo, was in Reptile Ocean last week, co-ordinating the removal of 27 illegal animals.

He confirmed there was a hole in the ceiling, where the fan used to be. Loyst also said that the ceiling beside the enclosure was covered in black mould.

Loyst said in his opinion, based on what he saw, it would have been easy for the python to escape.

The Barthe brothers were sleeping on a mattress about two to three metres from the enclosure, he said.