My take is that the police and FBI had been following this guy for weeks, maybe months and used some sort of technology to denonate the bomb while he was in a place that wouldn't harm anyone else.
Why they didn't get a search and arrest warrant before is beyond me.
If the timing of the police raid is correctly given, then you have to think that the feds were following him and his friends covertly to trace their contacts.
Whether the authorities set off the bomb is another matter. The story was that he approached the stadium gates three times, but was turned away. Were the gate guards warned about him, or was it sheer good luck that they happened to be stopping students to check them for alcohol?
I suppose the FBI could have spoken with the university president and asked him to think of some innocent-seeming reason to search everyone. That would explain why he is acting like an insider, in the know--also like an insider who thinks the American people are too stupid to be told the truth.
It seems to me that the cat is out of the bag, that the other Muslims must know that they are being watched, so the FBI could perfectly well let the media tell people the truth, that this was a terrorist plot that failed. That wouldn't give away anything the suspects don't already know.