We shouldn't jump to conclusions here. Are we forgetting the wrongful identification and accusations surrounding Ryan Lanza in the Sandy Hook Elementary school shooting? It was his brother Adam who was the shooter but it didn't stop the media from incorrectly reporting that it was Ryan and his picture was publicised all over the news, websites, blogs, Twitter and every possible media outlet you can think of.
While it's possible the person in the image could be the culprit, lets not jump to conclusions until we have some more solid evidence. Some people take off their backpack in crowds because it can get in the way, how do we know this isn't the case here? There are a thousand legitimate justifications for not having a backpack on you were seen carrying earlier.
I usually walk to the train station to commute to work in the mornings and take my backpack off once I get on so it doesn't get in the way of others. Now I know what people will be saying if the train gets blown up and they have imagery of me with a backpack on and without...