While emergency responders in Quebec, Canada sift through the wreckage for bodies which may never be found -- due to the intensity of the blaze caused by a train derailment on Saturday -- officials are focusing on why the train came loose from its overnight parking spot.

Five people are confirmed dead in the incident, which occurred when a train hauling 72 tanker cars carrying 30,000 gallons of crude oil each rolled seven miles downhill from an overnight parking spot and slammed into buildings in the small town of Lac-Megantic.

Up to 40 residents of the small town Lac-Megantic are still missing, and officials say their bodies may never be recovered. The five bodies found so far are severely burned, complicating the attempt to identify them. The Quebec Health Minister said the bodies will be sent to Montreal for forensic identification.

The train’s data recorder has been recovered from the crash. Donald Ross of Canada’s Transportation Safety Board said the focus of his agency’s investigation will be on how the train was secured.

Montreal, Maine and Atlantic Railway, the company that owns the train, said in a statement Sunday that a locomotive which had been left running overnight in order to hold the train in place had been shut down.

“One fact that has emerged is the locomotive of the oil train parked at Nantes station was shut down subsequent to the departure of the engineer who had handled the train from Farnham, which may have resulted in the release of air brakes on the locomotive that was holding the train in place,” the company said.

A company spokesman said the engineer had left the hand brakes on all the locomotives and the air brake, a high-pressure stop, on the lead engine but that some time after that, an unknown individual shut down the train.

After rolling downhill, the train derailed on a curve. The subsequent explosion and fireball destroyed dozens of buildings, including a popular nightclub which had an unknown number of patrons in it at the time of the blast.

Canadian Prime Minister Stephen Harper said Lac-Megantic looked “like a war zone.”