A provincial police spokesman said Friday he also expects investigators to return to the U.S. to gather more evidence for analysis in Quebec.
"We still have some work to do," Lt. Michel Brunet said about the cross-border investigation, which was conducted through Interpol.
"After analyzing (evidence), sometimes we need to go back just to clarify different things. That's what we're going to do."
Brunet said at least part of the police force's efforts took place at the Chicago-area office for Burkhardt's company, Rail World Inc. Burkhardt was chairman of Rail World subsidiary Montreal, Maine and Atlantic Railway, the firm at the centre of the catastrophe.
"We interviewed many American witnesses, people highly placed in the company like Mr. Burkhardt," he said.
A runaway train carrying volatile crude oil crashed in downtown Lac-Megantic last summer and set off huge fireballs, wiping out much of the town core and killing 47 people.
Earlier this week, Canada's Transportation Safety Board released its final report into the derailment, a document that criticized MMA for its role in the disaster and for its "weak safety culture."
The report, which Quebec police are analyzing, also singled out Transport Canada for its poor oversight of the rail industry, particularly at a time when oil-by-rail traffic is soaring in North America.
Montreal, Maine and Atlantic Canada, a subsidiary of the now-bankrupt MMA, and three of its employees have each been charged with 47 counts of criminal negligence causing death — one for each victim of the July 2013 accident.
The accused are engineer Tom Harding, railway traffic controller Richard Labrie and Jean Demaitre, the manager of train operations. Their charges have the potential for serious consequences: a conviction carries a maximum life sentence.
Since it is a company, MMA Canada could only face fines, if convicted.
Some locals who watched the accused enter the Lac-Megantic courthouse for their May arraignment said they hoped authorities would file charges against railway and government officials.
Brunet indicated Friday that the police investigation remains active, but that it's up to prosecutors to decide whether to make more arrests.
"There's always a possibility that more charges could be laid," he said, adding that Quebec police have interviewed 230 witnesses on both sides of the border and collected more than 1,000 pieces of evidence, including "tons and tons" of metal objects.
Police are keeping items like rails, train parts and the locomotives' black boxes because the criminal investigation remains active, he said.
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