Federal investigators told CNN Saturday that the amphibious tour vehicle that collided with a bus on a Seattle bridge had an axle that had been sheared off.
When the axle broke and whether it was a factor in the fatal crash is unclear.
Earl Weener of the National Transportation Safety Board told CNN the 1945 DUKW, or duck, boat lost its left front axle.
Five international students from North Seattle College were killed and about 50 other people were injured in Thursday's crash. Late Sunday, officials said a 20-year-old woman had died.