FOREST PARK, Ill.: Officials said nobody was at the controls of an empty commuter train that slammed into another train at a suburban Chicago station Monday, injuring dozens of commuters, but they don’t know how the train got moving.

Video footage shows that nobody was driving the four-car Chicago Transit Authority train as it rumbled the wrong way toward the train parked at the Harlem Avenue station about 10 miles west of Chicago. But investigators were trying to determine if it somehow started moving itself or if someone sent it on its way, intentionally or otherwise.

“If it wasn’t a goof or there is someone not telling us something that creates a big problem because if one train can start moving without anybody doing anything then it can happen to another train,” said Amalgamated Transit Union President Robert Kelly.

Kelly said he had never heard of a train simply starting to roll down the tracks. Not only that, but he said to start a train somebody would not only have to have a special key, but would have to know how to use it.

As many as four dozen people who were on the parked train were treated for minor injuries and released from hospitals, authorities said.

Firefighters from as many as a dozen local fire departments responded.