Because it doesn't matter if you're pure as the driven snow, you don't talk to anyone who is investigating you for a crime without an attorney present.
Good people confess to things they didn’t do and later find out it was not their fault, but find they are not effectively able to retract what they already have confessed to. Let’s say there was a problem with the accelerator being stuck...the conductor tries to fix the problem ending in the emergency brake solution...at 106 mph. Evidently he does have a head injury. He confesses, everyone has their responsible fixed idea. The NTSB completes it’s investigation and finds there was a maintenance problem with the accellerator, he’s still screwed because no one will be thinking about it a year from now when the NTSB finishes.
If he’s guilty, it is still up to the government to prove their case. I really doubt there will be much left unknown about him in the next few years while the civil and criminal cases are investigated. This case is going to make numerous lawyers a LOT OF MONEY. Unless he is a saint, he is going to be made to look worse than Satan himself.
DK