They're All Actors
Jeff Bauman, a Boston Marathon spectator, survived one of the explosions but lost both legs. A photo taken of Bauman being wheeled away after the explosion shows little blood, leading to the theory that he was an "actor" who had actually lost his legs in the military. (Another rumor was that some of the Sandy Hook survivors, who apparently attended the marathon, are actors who participated in the "staged explosion.") This confusing bit of misinformation (do these theorists really believe no bombs actually went off?) was quickly resolved when other photos (here and here) showed Bauman in pain and covered in blood and others with Bauman walking on two legs prior to the marathon.