If it was indeed an accident, they'll have to explain how the engineer screwed up and also how the automatic braking system failed.....
There is no automatic braking system. That stuff is still in the works on most railroads, and it was reported that this line has not implemented it yet. And the correct term, BTW, is "positive train control" or "PTC". The only other such devices I am aware of in use in the US is the deadman device that stops if the engineer leaves his seat or the alerter that must be acknowledged by the engineer at intervals or else it stops the train. Neither of those devices can stop the train automatically just because the train runs out of track.
Now, if the engineer screwed up, that will likely come out as the data recorder is downloaded. The crew's cell phone records will also be examined - you can be sure of that. The most recent version of inward facing cameras (I don't know if this line has them, but the major railroads are installing them) also has a cell phone detector that records any use of phones in the cab - which is grounds alone for permanent dismissal, even without any accident (truck drivers take note).
