A striking and graphic picture emerged from Boston of a man in a cowboy hat wheeling a badly injured man for treatment. His name is Carlos Arredondo.
"The device, the IED went down to the ground. The gentleman that I helped, he had a big fire going on his shirt. So whatever was in the IED was to make much damage."
Arredondo is a Costa Rican peace activist who has been through quite a lot in his life. After his son, who was a U.S. Marine, was killed in Iraq he tried to take his own life, but survived - only to see his other son take his own life in 2011.
He wears the pictures of his sons on his shirt. He was carrying a rolled up American flag, soaked with blood, as he spoke. And he was trembling - his hands, his whole body, still in shock.
When the explosion happened right in front of him and blew off the legs of a man nearby, it was Carlos Arredondo who saved his life by applying a tourniquet.
In a YouTube video that emerged later on Monday, a visibly shaken Arredondo told a questioner he found "blood, blood everywhere".
Despite the chaos around him -- he focused on that one man. "I just concentrated on that young man, tying up his legs, talked to him. He was conscious. I tried to let him know it was OK and then I managed to take him all the way to the ambulance. There were so many people begging me for help but I could only help one at a time. So I just helped that young man."
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