The man in the cowboy hat - Carlos Arredondo - photographed helping the injured following the Boston bombings has spoken to ITV News about the atrocity.
Carlos was a spectator at the race when he leapt into action, applying make-shift tourniquets to victims, which help save lives, including that of Jeff Bauman:
He was at the marathon to watch two runners honouring his dead sons. One, a solider, was killed in the Iraq war. His brother, so devastated by grief, later took his own life.
Carlos has kept hold of a United States flag he was waving at the marathon when the bombs exploded. It is now a blood-stained reminder of the attack.
Speaking of the those responsible for the attack, he says they are the "worst people":
Watch ITV News presenter Mark Austin's report in full: