Officials said Sunday that a mistake with the signal caused the terrible train crash in India that killed at least 275 people and hurt hundreds more. The accident, which happened Friday night and killed one person, involved two passenger trains. Sunday night, people were still working to clean up the wreckage.

A top Indian railway official told the Associated Press that one of the trains, a high-speed Coromandel Express, was given a signal to run on a line that was already in use, which caused it to crash into a freight train carrying iron ore. After the crash, the passenger train went off the tracks and onto another set, where it hit another train carrying more than 2,000 people. “The system is 99.9% error-free. But 0.1% chances are always there for an error,” Jaya Verma Sinha, a railway official, said at a press meeting, adding later that sabotage was not impossible. They said, “Nothing is ruled out.”