Police investigating the Lac-Megantic train disaster say they've visited the United States four times to seize documents and to interview witnesses — including railway chairman Ed Burkhardt.
A Sureté du Québec spokesman says investigators working the case also have plans return to the U.S. to gather more evidence.
Lt. Michel Brunet says the cross-border investigation was conducted through Interpol and at least part of it took place at Burkhardt's Chicago-area office.
Earlier this week, Canada's Transportation Safety Board released its final report into the deadly derailment — a document that criticized Burkhardt's railway for its role in the disaster and for its weak safety culture.
The now-bankrupt Montreal, Maine and Atlantic Railway and three of its employees have each been charged with 47 counts of criminal negligence causing death — one for each victim of the catastrophe in July 2013.
Brunet says the case is still open and Quebec prosecutors could still lay more criminal charges.