When the discovery of dangerous cracks in the Acela express trains shut down service along the northeastern corridor during spring 2005, Amtrak’s inspector general told Congress that the railroad company had narrowly averted a disaster.

But nearly two years later, Amtrak and the two companies that oversaw the trains’ maintenance are still battling over documents the inspector general’s office wants for its investigation into whether the problems were known before Amtrak first discovered them during a routine check in April 2005.