Mr. Parker, 33, was panhandling when the bomb exploded, according to local news reports. The force of the blast knocked him to the floor, but he was unfazed.
Rather than running for safety, he went to the aid of victims, comforting a girl who had lost her legs, wrapping her in a T-shirt, and cradling a dying woman in his arms.
Mr. Jones, 35, says he pulled nails out of children's arms and faces.
"Just because I am homeless doesn't mean I haven't got a heart, or I'm not human still," he told ITV News. "I'd like to think someone would come and help me if I needed the help," he said, adding that he had been overcome by an "instinct" to pitch in.