Well, that’s the classic use of the public safety exception. (Good work, by the way.)
Here, the guy already knows he doesn’t have to talk to police. It’s hard to find a college student in the country who doesn’t know that.
And a lot of robbers actually wouldn’t want a kid to find his gun and get hurt or hurt someone. A lot of them may be robbers, but are still human beings.
But THIS guy is a jihadi terrorist dirtbag. Asking him “where are the rest of the IEDs?” isn’t going to make him more likely to tell you by not mirandizing him. He WANTS innocent people to get blown up by them.
My hope would be that because he is injured and will possibly be drugged at the hospital, they can question him under the public safety exception (a questioning which, because he is in distress would not be allowed otherwise), and hopefully elicit information implicating any accomplices that they do not currently know about.
His statements implicating others during his questioning under the public safety exception can be used as probable cause to proceed against additional suspects.