I've read all manner of conspiracy theories surrounding this case. There is no reason to believe that the withholding of the Miranda warning has anything to do with anything other than the suspect's incapacity and/or the suspect's status as a terrorism suspect and the consequent intention to interrogate him with regard to the extent of future danger to the public. Until it is established definitively that there are no other conspirators, no other related dangers, then there actually is no right to remain silent.
Yes, of course. This is the process: Ensure that the public is safe from further terrorist, then turn attention to the past crimes.
I don't see the connection.