Hinrich's wallet was in his pants, with his ID. That's how they knew right away who he was.
The rest of him, above the waist, was blown to bits and splattered all over the busses in the parking lot.
That is bull about him "not wanting to hurt anyone else". (What his father said). A busdriver was a few feet away from him when the bomb went off. Hinrichs knew this because the driver spoke to him seconds before the explosion.
How did they know so soon who his roommate was, and where he was that evening so they could arrest him? Doesn't that strike you as odd? Wouldn't that normally take hours, not minutes? And, bear in mind, they still haven't positively id'ed him--they're waiting on dna tests.