(CNN) -- The sleepover went horribly wrong.
Two boys, aged 5 and 7, were found dead Monday morning in an apartment above a pet store in a small Canadian town.
Their suspected killer is a python that reportedly weighs about 100 pounds.
Early indications suggest that a snake escaped its enclosure in the store, got into the ventilation system, then the apartment, and strangled the two boys, the Royal Canadian Mounted Police said.
The owner of the pet store in Campbellton, New Brunswick, says he came upon an awful sight when he entered the living room where the boys were staying.
"I thought they were sleeping until I seen the hole in the ceiling. Everything had fallen. And I turned the lights on and I seen this horrific scene," Jean-Claude Savoie said in a phone interview with the Canadian website Global News.
Savoie said he believed the snake had fallen through the ceiling as it slithered through the ventilation system.
He said he located the reptile in a hole.
"I pinned him down and put him in a cage," he said.
Neighbor expresses shock
Police say they now have the python in their possession. Autopsies on the boys' bodies will be performed Tuesday.
Canadian broadcaster CBC reported that the python is between 11 and nearly 15 feet long and weighs more than 99 pounds.
A neighbor, Diane Fournier, has lived on the same street as the pet store for 12 years. She described the deaths as "shocking."
"I knew the kids. They were brothers," she said. "They played in my yard with my dogs all of the time."
Fournier sent CNN a photograph her husband took of the pet store. It showed police cars, cones and yellow tape blocking off the area.
The store, Reptile Ocean Inc., offered condolences on its Facebook page Monday before the page was shut down.
A 1996 report by the animal protection charity Zoocheck and the World Society for the Protection of Animals listed Savoie as the owner of Reptile Ocean.
It described him then as "a young enthusiastic amateur collector who has only recently embarked on this commercial venture."
'I can't believe this is real'
According to Global News, Savoie said that the two boys were the children of his best friend and that they often slept over at his apartment.
"I have so many mixed emotions right now it's ridiculous," he said. "I can't believe this is real."
Deaths caused by large constrictor snakes like pythons are fairly rare.
The Humane Society documents 17 people who have died in incidents in the United States related to the snakes since 1978, 12 of them since 1990.
But scores of adults and children have been hurt in attacks by the reptiles, the society said in a report this year.
"Children, parents, and authorities are finding released or escaped pet pythons, boa constrictors, and anacondas all over the country, where they endanger communities, threaten ecosystems, and in many cases suffer tragic deaths," the report says.
In Canada, a man in Ontario was killed in 1992 by his pet python, the Globe and Mail reported, citing Melissa Matlow, a spokeswoman for the World Society for the Protection of Animals in Canada.
By Jethro Mullen
CNN's Kevin Conlon contributed to this report.