The death toll rose from 13 to 15 with the discovery of two more bodies after the explosion and inferno produced by the derailment of a train carrying oil near Montreal. Around 40 people are still missing.
Quebec police are looking for "evidence that might allow the filing of criminal charges," said police inspector Michel Forget, yesterday. He did not specify against whom.
Standing 200 meters (yards) from the scene of the disaster, he said the hypothesis of criminal negligence was "under consideration."
"We are very hopeful we will find more bodies," said Forget.
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Residents of the small Quebec town of Lac-Megantic, part of which was flattened by the blast and subsequent inferno, began returning to their homes.
The explosion unleashed a wall of fire that tore through homes and businesses in Lac-Megantic, located east of Montreal near the US border.
The chairman of the Montreal, Maine & Atlantic Railway, Edward Burkhardt, accused firefighters of releasing the train's brakes when it was stopped in Nantes, around 13 kilometres (eight miles) west of Lac-Megantic, for a crew changeover.
Burkhardt told the daily La Presse that Nantes firefighters "showed up and put out the fire with a fire extinguisher. To do that they also shut down the first locomotive's engines. This is what led to the disaster."
He explained that the train's brakes were powered by the locomotive and would have disengaged when it was shut down, causing the driverless train to start rolling downhill towards Lac-Megantic.
By the time the company was informed of the shutdown, the train -- en route from the US state of North Dakota to a refinery in Canada's eastern New Brunswick province -- had already reached the town, he said.
Nantes Fire Chief Patrick Lambert however dismissed Burkhardt's accusations, saying the 12 firefighters who responded to the locomotive engine fire followed all of the proper procedures.