By Richard Valdmanis and Julie Gordon
LAC-MEGANTIC, Quebec, July 9 (Reuters) - Canadian police on Tuesday said they had opened a criminal investigation into the train explosion that likely killed 50 people in Lac-Megantic, and some 200 officers were scouring the town's devastated center for clues.
Inspector Michel Forget said police did not believe terrorism was involved when a runaway train hauling 72 cars of crude oil barreled into town early on Saturday, derailed on a curve and exploded into a huge fireball that destroyed the center of the lakeside community.
"I will not speculate on the evidence that we've recovered because (it is) secret," Forget said. But he indicated that some evidence might point to "criminal acts."
"We don't think the terrorism aspect is a part of that," he added. "Criminal negligence might be one of the leads we are looking at."
Almost a third of the town's 6,000 residents were evacuated from their homes as firefighters from Canada and the nearby U.S. states of Maine and Vermont struggled to bring the massive blaze under control. Just over half have been allowed back.
Montreal Maine & Atlantic, which owned the train, is one of many North American railroads that have vastly stepped up crude-by-rail deliveries as producers seek alternatives to pipelines that have been stretched to capacity by higher output in Canada and North Dakota.
The oil in the train that crashed was being transported from the Bakken fields of North Dakota to eastern Canada.
Police have found 15 bodies, but residents hold out little hope that the 35 or so people still missing will be found alive in an incident that could turn into North America's worst rail disaster since 1989.
Officials from the Transportation Safety Board of Canada said more than a dozen investigators were examining every angle of the accident, although even they had not yet gained access to the central "red zone."
Key elements of the TSB probe, led by investigator Donald Ross, will include the strength of the widely used DOT-111 cylindrical tanker cars that carried the crude, as well as how the train, almost a mile (1.6 km) long, was secured for the night on a stretch of rail line in Nantes some eight miles (13 km) from Lac-Megantic.
Industry rules say engineers must set enough of a train's handbrakes to ensure it cannot move, and then test that they have done a proper job. Ross said his team cannot check whether the brakes were set until it can enter the center of town and examine the pile of derailed cars.
Montreal Maine & Atlantic Chairman Ed Burkhardt told Reuters the company had followed protocol, using the same standard as Canadian Pacific Railways, Canada's No. 2 railroad.
The company had always put a lot of effort into safety, he said in an interview with Canadian Broadcasting Corp.
"Obviously we've blown it all with this tragedy," he said.
Ross said the train was on a 1.2-percent grade when it started sliding toward Lac-Megantic, a relatively steep grade in railroad terms.
He said the train line lacked a signal system that could have warned the dispatcher of a runaway train, and that although all trains are required to have automatic braking systems for runaways - called dead man switches - they only work when the train's locomotives are running.
Most of the railcars now lie where the rail line used to run, crumpled together like the squished-up links of a chain.
"If we think there needs to be a safety message out to the industry that they need to beef things up, we're going to do it," Ross said.
The TSB and its U.S. equivalent, the National Transportation Safety Board, have long urged tougher rules for the DOT-111 cars.
But nobody knows if stronger cars would have prevented the disaster, which involved a train that Ross said was traveling "well in excess of its authorized speed."
The train was parked in nearby Nantes, Quebec, on Friday night when one of its engines, which had been left running to ensure the air brakes had enough pressure, caught fire. Local firemen turned off the engine, put out the fire and went home.
The unattended train then started moving downhill toward Lac-Megantic, and derailed and blew up in the town center at just after 1 a.m. (0500 GMT) on Saturday.
Montreal, Maine & Atlantic says shutting off the engine caused the air brakes on the locomotive to lose pressure, possibly allowing the train to break free.
But a briefing from Transport Canada, which regulates railroads, focused on the train's handbrakes, a separate system that locks individual locomotives and railcars in place. It highlighted how unusual it was to leave an unattended train on a main line.
Experts see handbrakes as crucial for trains that are parked overnight, given that air brakes need power from a locomotive.
With fires out and authorities probing the center of the blast, the death toll is expected to climb. The coroner's office asked relatives of the missing to bring in brushes, combs and razors so experts could extract DNA samples from strands of hair.
"They know their loved ones were there, on the site. Most of them are now waiting for confirmation - because that makes it official," said Steve Lemay, the parish priest of Lac-Megantic, who has been meeting with families. "It's clear that they are not waiting for the missing to return."