That's speculation. What is known is a bomb exploded and a student is dead. A bus driver saw him sitting on a bench before something went BOOM. A female witness saw two middle-eastern running away toward the stadium immediately after the explosion.
If he was sitting on the bench as reported, someone could have left the bomb on the bench either before he sat down or after, then departed. The sweeps with bomb-sniffing dogs prior to the explosion could have foiled any plans (by whomever) to take the bomb(s) into more densly packed area. There apparently was concern earlier that additional security and sweeps were necessary. Whoever was walking around with a backpack of explosives would have sought other methods for placing it, or getting rid of it.
My speculation makes just as much sense (to me at least) as any that has been reported. Reports from the investigators, media, and university president are in conflict with someone who knew the victim better than any of the former. So everyone will have to make their own choice about who to believe.
"A female witness saw two middle-eastern running away toward the stadium immediately after the explosion."
Another interesting detail that I haven't seen before. Where did you learn this?
"If he was sitting on the bench as reported, someone could have left the bomb on the bench either before he sat down or after, then departed."
So, any explosive materials found in Hinrich's dorm room were planted by these Muslims on the same hall, along with any Muslim literature, making him an innocent victim? Framed, in other words?
That sounds a bit implausible to me. But, I suppose it's not completely impossible. If Hinrichs just happened upon a backpack or something, by accident, somebody would really have to hustle back to the dorm to pull this off, though. I'd think witnesses there would be a problem.
Regardless of your ethnicity, where would you run if a bomb went off in your vicinity, towards the bomb or away from it towards a large relatively secure building like a stadium where you know you could find police to report the explosion. Also, if you are smart and not involved and you do happen to be middle eastern in appearance what do you do, do you run away and instantly become targets of a man hunt or do you run towards the stadium and the police. Duh? Look what happend in London to the guy that ran the wrong way.
Now it's getting real interesting.