KANSAS CITY, Mo. — As Jeff Bauman waited for his girlfriend to cross the finish line of the Boston Marathon, a young man with a backpack bumped into him.

The young man looked out of place in the crowd and didn’t seem to be watching the marathon, Bauman thought. Even after the young man set down his backpack, Bauman turned his attention back to the race — he didn’t want to miss seeing his girlfriend, Erin, complete the 26.2-mile run. He also remembered feeling a sense of security being in Boston.

A few minutes later, Bauman heard three pops and saw a flash of light. Suddenly, he was on the ground. “It smelled like fireworks,” he recalled.

Bauman saw that his legs were “obliterated.” He remembers thinking that he was going to die, but he felt a strange sense of calm. A bystander in a cowboy hat, Carlos Arredondo, rushed to help him, and he was soon taken to the hospital. He survived, but both of his legs were amputated above the knee.

What the 27-year-old had just lived through was the Boston Marathon bombing on April 15, 2013, and he played a pivotal part in identifying one of the suspects.

Bauman shared his powerful story in a keynote presentation at the National Association for Pupil Transportation's (NAPT's) 2016 Summit in Kansas City on Sunday morning.

In the hospital, Bauman gave the FBI and police a description of the bombing suspect he had seen, Tamerlan Tsarnaev, who was eventually tracked down and killed in a shootout with police. Bauman also later testified in the trial of Tsarnaev’s younger brother, Dzhokhar Tsarnaev, who was convicted in the bombing that killed three people and injured more than 200.

Meanwhile, Bauman said that he endured a time of “excruciating pain” after the attack as he underwent surgeries. He was fitted for prosthetic legs and went through physical therapy to learn to use them. About two months after losing his legs, he stood up for the first time.

Bauman became emblematic of the “Boston Strong” slogan in the wake of the bombings. He was invited to throw the first pitch at a Red Sox game at Fenway Park. He attended Erin’s next race, in Portland, Maine, and overcame his fear of returning to a finish line. Then in the next Boston Marathon, in 2014, Bauman returned to the site of the bombing — escorted by the mayor’s police detail — to cheer on the runners.

As he spoke to NAPT attendees, Bauman remained upbeat and elicited laughs from the crowd, but he acknowledged that the years after the bombing came with intense struggles that he had to work through. For one, he said that he overindulged in alcohol, but now he’s five months sober.

Bauman cowrote a book about his experience, called Stronger, which is being made into a film. He and Erin are now married and have a daughter.

In introducing Bauman, NAPT Executive Director Mike Martin said that his story is inspiring and powerfully illustrates the “If You See Something, Say Something” message that the Transportation Security Administration (TSA) promotes.

The presentation came a day after an extensive security training program that NAPT held with TSA for Summit attendees.