I think the purpose of the "regular guy" picture was to reiterate the frightening possibility of "home-grown" terrorism perpetrated by your everyday normal "boy next door". I don't object the choice of picture: people know what he did and the horror he caused. I think the article's purpose is to go beyond the acts and examine what inspires a "normal", fun loving guy like Dzhokhar to do something so horrific.

Now whether or not it belongs on the cover is certainly debatable.