Lac-Megantic, Quebec (CNN) -- Canadian authorities have found evidence that a train that crashed in Lac-Megantic, Quebec, was tampered with, provincial police Capt. Michel Forget said Tuesday. There have been many questions about the train explosion that wiped out a swath of Lac-Megantic's downtown, killing at least 15 people. As of Tuesday evening, 35 people were still missing, Forget said. Investigators had earlier said that they are trying to figure out if the train's brakes were disabled before it barreled at a dangerous speed into the Quebec town, derailed and burst into a deadly inferno. Firefighters in the nearby town of Nantes put out a separate blaze on the train shortly before it crashed into Lac-Megantic early Saturday. Ed Burkhardt, chief executive officer and president of Rail World, the parent company of the Montreal, Maine & Atlantic Railway, has told media outlets there's evidence the engine powering the brakes was shut down at some point. Pressed to elaborate by CTV, Burkhardt wrote Tuesday in an e-mail exchange, "We are now aware the firefighters shut down the locomotive. By the time (Montreal, Maine & Atlantic) people found out, it was too late." In earlier comments to the Montreal Gazette, he said the matter needs further investigation, and his company has begun an internal inFuiry.