Never mind the obvious frame-up potential of it happening at a MLK parade, I’m very dubious of the “bomber” leaving a T-shirt in the same backpack. He decided to use a backpack that he’s had for quite some time, and “forgot” he left “his” t-shirt in it?
Ha, excuse me, TWO shirts in the backpack, the other one says “Treasure Island Spring 2009” but doesn’t look fancy enough to come from the casino IMO:
http://www.spokesman.com/stories/2011/jan/18/fbi-says-backpack-spokane-parade-route-was-bomb/