(CBS News) A video of one marathon runner knocked to the ground just as the first bomb exploded near the finish line of the Boston Marathon .
The man in the video is Bill Iffrig, a 78-year-old runner who was just about to complete his third run in the Boston marathon, before his legs buckled under him. He spoke Monday night about the moment he felt the blast.
"Shock waves just hit my whole body and my legs just started jittering around. I knew I was going down," Iffrig said.
A veteran of 45 marathons, Iffrig traveled from his home in Washington State to run the Boston Marathon. Iffrig recalled, "I was just approaching the last straightaway to the finish line and I'd had a good day and I was feeling really good."
Fewer than 20 feet from the finish line when the explosion forced him down, Iffrig says his injuries were minor.
"Didn't feel any severe pain, but as I rolled over I saw a little scratch on my leg," he said, "but nothing too bad so I just laid there momentarily."
Iffrig was immediately surrounded by first responders, and then helped up by marathon officials. As the wounded were taken away from the scene and the remaining runners forced from completing the race, Iffrig walked another half-mile to meet his wife at their hotel -- right after he crossed the finish line.
A marathon official helped carry Iffrig to that finish line, but the half-mile walk to reunite with his wife, he did on his own.
Watch Terrell Brown's full report above.