SEOUL, South Korea (AP) — The subway operator in the South Korean capital says a train received a faulty ‘go’ signal before it crashed into another train, slightly injuring 249 people.

Chang Jung-woo, CEO of Seoul Metro, told reporters Saturday the case is still under investigation but the malfunction in the automatic distance control system is presumed to have caused Friday’s crash.

Chang said “Normally, the signal should be given in the order of ‘stop’ and then ‘caution.’ But at the time of the accident the signal was given in the order of ‘stop,’ and then ‘go-ahead’.”

The driver of the moving train applied its emergency brakes after noticing the stopped train ahead, but wasn’t able to halt in time.