Bruce Mendelsohn was attending a post-race party in an office building just above the blast site when an explosion knocked him to the floor.
"There was like a flash, then a giant boom. The concussion blew me off the couch onto the ground," he said.
The former Army medic rushed outside and found blood, glass and debris everywhere and began applying pressure to "gruesome" wounds.
"This stuff is more like Baghdad and Bombay than Boston," said Mendelsohn, who works at the Massachusetts Institute of Technology. "It was pretty terrifying."
Phil Kenkel was approaching the finish line when the two explosions happened just moments apart. The first made him wonder if it was a prank, the second stirred "sheer terror."
The second bomb "went off virtually right beside me. About the only way out of that area was straight ahead," said Kenkel, of Stillwater, Okla.
"The glass was out of the building, and there was obviously a big hole in the crowd. You realize there must have been people there that were knocked down."
Kenkel called his wife to let her know he was all right.
"He wasn't hurt, which is a miracle, I guess," Evelyn Quillen said.
Peter Gravelle was in the VIP seating area at the finish line, waiting for his son and granddaughter when the blasts happened. He saw one victim sail through the air — then what he believed was a severed limb.
"I thought I saw an arm," he said.
His wife, Mary, said she'll never forget the horror of what she saw.
"My heart breaks for all these people," she said. "They actually fell down in the road. The poor souls, yelling for help."
The couple's son and granddaughter were unhurt.
A Kansas surgeon had finished the race moments before he ran to help the wounded.
The first blast came about 30 seconds after Dr. Chris Rupe, of Salina, Kan., crossed the finish line. At first, he thought the sound came from a building or grandstand collapsing. He hurried to see if he could help and spent about an hour in the medical tent treating the wounded.
After that, most had been transported to hospital.
"I'd just run 26 miles. I was starting to get tired," Rupe told The Salina Journal. "There were a lot of great people who were there. There are a lot of good people in the world."
Emily Biglin Valentine thanked God she ran a good time.
The Novi, Mich., woman's husband and good friend were in the exact spot of the explosions just a half-hour earlier. They heard the explosions as they walked to a train. It sounded like cannon fire.
"When I finished I was so elated, and I said, 'I'm doing that again.'"
Now she doesn't think she'll go back.
Thomas Fabian II's father had finished the race shortly before the explosions, but his mother was still on the course miles back.
Fabian, of Port Charlotte, Fla., said his mother, Carol, ended up at a cafeteria and chapel on the campus of Boston College with a crowd of other runners. She had a hard time reconnecting with her husband.
Fabian's parents have run nearly 100 marathons in the last five or so years, he said, and were scheduled to fly from Boston quickly to compete in this coming weekend's London Marathon.
"I'm not sure if they're going to go now," he said.
Norwegian Janicke Ekelberg had also finished the race and was walking back to her hotel when she heard the explosions.
"At first I thought it was a salute," Ekelberg told Norwegian broadcaster NRK. "But then I saw the emergency vehicles coming in. Fire trucks, ambulances. Then we realized something wasn't right."
Tracy Eaves had just crossed the finish line moments earlier to finish her 39th marathon, collected her medal and called her husband back in Niles, Mich., when she felt and heard "this huge shaking boom."
Eaves told her husband she thought it was a celebratory cannon blast. After the second blast, she started to panic.
Race officials quickly ushered her and other runners from the scene. She eventually made her way back to her hotel.
"You're so happy and excited to finish. You're ecstatic. You get your medal. You get your Gatorade and — boom."
Associated Press writers Erika Niedowski in Providence, R.I.; Larry Lage in Detroit; Sean Murphy in Oklahoma City, Okla.; Tim Reynolds in Miami; Karl Ritter in Stockholm; and Michael Rubinkam and Meaghan Barr contributed to this report.
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