Is This an Act of Sabotage?

There is some evidence it may have been a mechanical issue. The NTSB referenced the video at a news conference earlier this week. We have attained two videos which show preliminary indications of mechanical issues on one of the rail car axles. There are sparks flying out and you can clearly see them in the video from underneath one of the cars at the rail. Was there something wrong with that axle? So it could just be a mechanical problem. I wish they did. It's not a rare incident. They don't happen all the time, but it happens often enough that there's the possibility of just a mechanical failure is there.