I wonder if the McDonald's employee really recognized him from those couple of off-angle photos or if Mr. Mangione himself initiated the action in order to let someone "deserving" collect the reward. It seems to me that he wanted to be caught, and the amount of evidence that he was carrying on him is obviously meant to establish his identity beyond any doubt. The amount of meticulous planning he undertook for the actual shooting contrasts with the trail of evidence that he kept dropping along the way. He would've basically never been found if he had just worn a pair of sunglasses.