Others show a man in a hat named Carlos Arredondo doing just the opposite.
One of the day's most gruesome but moving photographs, taken by Charles Krupa of The Associated Press, shows Arredondo pushing a man, identified as 27-year-old Jeff Bauman, in a wheelchair. Bauman's lower leg was blown away by the bombings, exposing his bloodied bones.
Due to the graphic nature of the image, it was sent to Associated Press members in two versions. In one, the leg is cropped out, and in the other, the damage is shown, said Santiago Lyon, AP vice president and director of photography. (Many AP photos are sent directly to news websites with no outside filtering, but this picture was held back so editors could make their own decisions about whether to use it. PEOPLE.com published the cropped version.)
"Different markets have different tolerances for violence and gore," Lyon said. "We're pretty sure that parts of the world will make good use of it. We didn't want it to get out in the flow with no human intervention."
Capturing a HeroThe image memorializes a moment of heroism for Arredondo, 52, who ran from his seat in the bleachers to help victims when he heard the blast. Along with John Mixon – who runs an organization for fallen war heroes of Maine with Arredondo – he ripped and tore through fencing to get to those who were hurting.
"We needed to help this man who lost his legs get into a wheelchair," Mixon tells PEOPLE. Once Bauman, was secured, Arredondo ran.
"Carlos was talking to him, saying, 'My name is Carlos. We are going to help you,'" recalls Mixon. "The man was mumbling, saying, 'Help me. I can't feel my legs.' Carlos was saying, "You're going to be all right.' "
Arredondo, after all, is no stranger to tragedy. The American Red Cross volunteer and peace activist came to the marathon to honor his son who was killed in Iraq during a 2004 firefight, reports ABC News. (His other son committed suicide.)
At the end of the day, Arredondo's hat was gone, perhaps lost in the chaos, and Mixon doesn't know where it is.
"He was a real hero," added Mixon. "He didn't know if another bomb was going to go off. He just said, 'God help us. We need to help them.'"
With reporting by CAITLIN KEATING and THE ASSOCIATED PRESS