Here is a long but informative link on why he didn't have his Miranda rights read.
https://www.fbi.gov/stats-services/p...1/legal_digest
Long story short there was a ruling back in the 80's that allows questioning w/o a miranda warning when public safety is at risk.
In this case trying to detemine if there were more terroists planning more bombings or more bombs planted.
According to this article I think it will hold up.