Shah and his running mates heard a loud boom, but weren't sure what had happened. So they continued toward the finish line. Then came the second blast, local WCVB Boston TV reported.
"All the runners and spectators started running towards us, away from the finish line. But my entire family, my wife, my daughter, my parents and my sister were all at the finish line. So I started running toward where I heard the boom," Shah told the station.
Concerned for his family, he had no idea what he was about to witness.
"People with traumatic amputations, one leg, both legs, it just looked like everyone was in shock. If you look into the victims' eyes, they didn't really know where they were. I've never seen that quantity of injury in one place," Shah was quoted as saying.
Compelled to help, he said: "I just tried to see if anyone needed any emergent care, if anyone was bleeding out. We put on some makeshift tourniquets."
But within a minute, he said, emergency physicians were on site, attending to every victim.
"As soon as the area was stable with lots of personnel, I tried to find my family, because my biggest concern was that one of the faces that I'd see would be theirs," Shah said.
Thankfully, his family was fine. But they'd all come frighteningly close to tragedy.
"They didn't leave the area even though they were being told to evacuate. They were just hoping that I would show up. They were only 25 yards from where the last blast was," Shah told WCVB Boston.
Shah said he was amazed by the quick and professional response from emergency volunteers and physicians. By the time he left to find his family, he said there were two to three personnel for each victim.
Shah's story represents the heroism of many other medical professionals who were close by when the terror began: doctors, nurses and paramedics who were running, spectators in the stands or waiting at the finish line to treat exhausted runners, CNN commented.
Time is vital in saving lives, noted CNN Chief Medical Correspondent Sanjay Gupta, another Indian American. Doctors call the first 60 minutes the "golden hour" in trauma response, he said.
Within the first 15 minutes, 15 patients were at Brigham and Women's Hospital, a Level I trauma centre, Gupta said. Seven operating rooms were immediately cleared for the nine patients needing surgery, he said.
