The heads of Amtrak and the National Transportation Safety Board were called in front of a congressional committee Tuesday to answer questions about the May 12 Amtrak crash that killed eight people.

The NTSB, which released a report detailing the crash on Tuesday, said it found no apparent mechanical problems with the train. The report concluded that the train was traveling 106 mph heading into a 50 mph curve and hinted that the derailment could have been caused by a “human factor.”