Italian and EU flags flew at half-mast at the office of Italian prime minister Silvio Berlusconi, who said Italy joined the U.S. in condemning "these monstrous criminals who have demonstrated a vile and brutal affront against humanity, " The Associated Press said.

CNN: Europe reacts with shock and horror

Arredondo, a peace activist and sometime cabbie and truck driver who was watching the race from the finish line, rushed into the mass of mangled humanity, where a dramatic Associated Press photo caught him pushing a wheelchair with a victim who lost most of his lower legs in the attack.

NPR: Marathon Rescuer Gets Attention From Press And FBI