Investigators are zeroing in on speed as a cause of Monday morning's train derailment that killed three passengers in Washington state, ABC News reports.

The National Transportation Safety Board said the Amtrak train was traveling 80 mph in a 30 mph zone, according to the black box recovered from the accident. The crash killed at least three people and injured over two dozen more when it derailed going over a bridge near Dupont, Washington. The crash sent train cars hurtling off the bridge and onto the highway below, according to ABC News.

Authorities said that the three people killed were all passengers on the train. At the time of the crash, there were 86 passengers and crew on the train. Several drivers were injured on the road below the crash, but no one was killed.