That fellow (Jeff Bauman) who lost both legs below the knee, the one whose femoral artery is being pinched shut by Carlos Arredondo as he's being wheeled away from the incident, identified his attacker. From Bloomberg:
"Minutes before the bombs blew up in Boston, Jeff Bauman looked into the eyes of the man who tried to kill him.
Just before 3 p.m. on April 15, Bauman was waiting among the crowd for his girlfriend to cross the finish line at the Boston Marathon. A man wearing a cap, sunglasses and a black jacket over a hooded sweatshirt looked at Jeff, 27, and dropped a bag at his feet, his brother, Chris Bauman, said in an interview.
Two and a half minutes later, the bag exploded, tearing Jeff’s legs apart. A picture of him in a wheelchair, bloodied and ashen, was broadcast around the world as he was rushed to Boston Medical Center. He lost both legs below the knee."
-- http://www.bloomberg.com/news/2013-04-19/boston-bombing-victim-in-iconic-photo-helped-identify-attackers.html