Police sift through 'crime scene' days after Quebec train crash LAC-MEGANTIC, Quebec (Reuters) - Investigators sifted through the charred remains of Lac-Megantic's historic downtown early Wednesday morning, as they searched for clues into what could turn out to be North America's worst railway disaster since 1989. Police said they are investigating whether Saturday's derailment and subsequent explosion - which leveled the center of the lakeside Quebec town killing at least 15 and probably dozens more - involved foul play or criminal negligence. We are conducting a criminal investigation. We are not neglecting anything so far," provincial police inspector Michel Forget told reporters on Tuesday evening. He added that some 60 officers would continue to work through the night gathering evidence and searching for remains. Canada's Transportation Safety Board said it was looking into whether the train's operator - Montreal, Maine and Atlantic - followed proper safety procedures in the hours before the unmanned 72-car train carrying crude oil rolled down a hill and slammed into town. The incident forced some 2,000 people, or roughly a third of the town's population, to leave their homes and seek shelter in local schools or with friends and family. As firefighters contained the blaze, many of the evacuees were allowed to return to their homes, where they found a mix of relief, emotional distress and unexpected problems. "After that tragedy, after watching that fire burn half the downtown, we are happy to be back home," said Denis Leveille, 57, who spent the day on his front porch visiting with friends. But we're not really settled in, because we don't have electricity right now. Our only power is that yellow cord there," he said, pointing to an extension cable running out a front window and across the yard to a neighbor's house. We need that for the fridge and the coffee maker - so we have coffee in the morning and beer at night. But others were not as lucky. With parts of the town still considered dangerous - and part of it still a crime scene - emergency officials could not say when the remainder of the evacuees, about 800 people, would be permitted home. For some of the remaining evacuees, who waited patiently at the perimeter for days, watching others allowed through was the last straw. A small group lashed out angrily at police, demanding that they be let back into their homes just a few meters away. "We just want to go home," said one man, who was later ushered away by police. We have rights in Quebec, no? Still others chose to stay far away from the once-picturesque downtown, in part because of the emotional strain of being so close to the blast zone. Caroline Rancourt, a 37-year-old single mother, said she was at work at the Musi-Café, a favorite local hangout, hours before it was leveled by the runaway train. Eyewitnesses said the bar was packed when the train hit and burst into flames. "It was the screams that woke me," she said. I remember I was half asleep and I heard the cries and thought, 'It's night, why are there kids screaming?' "Then (there was) the sound of fireworks, and then after that it was all so fast," she said, struggling to hold back tears. We left and I didn't yet know what all had happened at the Musi-Café. She took her two children, 4 and 5 years old, to her mother's home on the other side of the lake. While she was allowed to return home early Tuesday, she opted not to stay. "It hasn't really hit me yet," she said. I was busy with getting my kids somewhere away from all this, so it would be less traumatic. I did what I had to do. MMA executives have said they believe the train's air brakes failed while it was parked in the neighboring town of Nantes, after firemen shut down the engine to put out a fire that erupted on Friday night. But it remains unclear whether the train's conductor had set enough hand brakes - which are meant to hold a train in place even if the air brakes fail - before he left the train for a shift change shortly before the fire broke out. MMA, which is headquartered in Chicago, has a long history of accidents in Canada, according to Transportation Safety Board data, which shows 129 accidents, including 77 derailments - some of them minor - since 2003. A TSB official said she could not immediately say how that compared to other rail operators in the country.