BOSTON, April 16, 2013— -- Bill Iffrig of Lake Stevens, Wash., was just feet away from the finish line at the Boston Marathon Monday when an explosion knocked him to the ground. Unaware of what had happened behind him, the 78-year-old marathoner thought it was his "last trip."
The widely circulated photo of Iffrig's being knocked to the ground by the bomb blast has become the hallmark image of the Boston Marathon attack that has left three people dead and 145 injured, at least 17 of them in critical condition.
"I could see the finishing line and I was about 15 feet when this horrendous explosion occurred," Iffrig told ABC News Monday night. "My whole body was just crumpling. I thought this was going to be it. I thought this was my last trip. I had no idea what was going on."
Iffrig scraped his knee and was able to cross the finish line, aided by volunteers.
"I didn't think about any possibility of another bomb going off by the finish line," he said. "And then after I was up and walking over there the other bomb went off. It was loud, I mean really loud. When I got back here, I could hardly hear anything."
The second blast occurred about 50 to 100 yards away from the initial blast.
After the race, Iffrig walked six blocks back to his hotel, still not sure what transpired.
The runner's son, Mark Iffrig of Seattle, told The Associated Press he was tracking his father's race progress online and didn't realize what had happened until he went on Facebook to post about his dad finishing the race. He quickly turned on the TV and called his dad.
COMPLETE COVERAGE: Boston Marathon Explosion
"It's horrible," Mark Iffrig said, adding that he recognized his father from the widely distributed photo showing him on the ground, surrounded by police officers and race officials. "He said it was quite a concussive blast. He was a little dazed. Someone helped him up."
Iffrig said his father is an avid runner who has raced in a number of marathons.
"He's a hell of a runner," he said. "He's run a lot and he's fast."
Bill Iffrig finished the race in three hours and 50 minutes.
The Associated Press contributed to this report.