A criminal investigation is underway into the deaths of two boys who were killed by a python that escaped its enclosure at a pet store in Canada, police said Monday.

Police arrived at the apartment in Campbellton, New Brunswick, at 6:30 a.m. and found the two boys, aged 7 and 5, dead. A friend of the brothers was sleeping in another room and was unharmed, according to Police Const. Julie Rogers-Marsh.

Royal Canadian Mounted Police (RCMP) officials told the Canadian Broadcasting Corporation that the owner of the pet store, Jean-Claude Savoie, was hosting the two boys for a sleepover with his own son. Savoie reportedly discovered the bodies of the two boys and called the police.

Rogers-Marsh said the snake, described as an African rock python, was believed to have made its way into the apartment through the ventilation system overnight.

The snake was captured and is in the possession of police. Calls to the pet store were not returned Monday. In New Brunswick, pet stores are allowed to sell non-venomous snakes of up to three meters, or just under 10 feet, in length.

“It’s very, very unusual and very tragic and difficult for everyone involved,” Rogers-Marsh said.

Autopsies will be performed on the two victims on Tuesday.

Read more: Fox News