Here's my hot take for the day
The DoJ will claim presence of a political manifesto means its a terrorist attack and he will be tried as a terrorist in secret or in closed court. And if possible without a civilian jury.
Could happen I guess, but I don't think it'd change things too much one way or the other. Once he pulled the hit and got taken alive I think he's achieved max class awakening as can come from the incident. Either he gets his day in the sun to spread his gospel or they do something like you theorize and the conspiracy theories and the like (somewhat rightfully) go nuts on 'what don't they want you to know'?