A viral video from Monday’s Boston Marathon shows Marine veteran Micah Herndon crawling across the finish line to complete his race after suffering from severe leg cramps.

The 31-year-old Marine vet told the Record-Courier that he entered the Boston Marathon in honor of three comrades who lost their lives in an IED explosion in Afghanistan in 2010.

It was an IED explosion he survived.

“Survivor’s guilt, it’s real,” Herndon told The Washington Post. “I definitely have it because I was the lead machine-gunner on that convoy and I didn’t see that bomb that was buried. I live with that every day.”

A veteran of the wars in Iraq and Afghanistan, Herndon deployed in 2010 to Marjah, Afghanistan, with the “Lava Dogs,” a nickname for 1st Battalion, 3rd Marines, headquartered out of Hawaii, the Record-Courier reported.

During that deployment, Herndon’s unit struck three IEDs, the first one claimed the lives of two friends Mark Juarez and Matthew Ballard, and a British journalist Rupert Hamer, according to the Record-Courier.

The third strike tore through Herndon’s Mine-Resistant Ambush Protected vehicle, launching him from the the gunner’s turret and knocking him unconscious, the Record-Courier reported.

Herndon said he now finds solace in running.

“I went from being in a war zone one day to trying to live a normal life the next day. We were going on three or more missions a day, constantly on guard and when I got back home, I was still in that mode. I never will be able to get over it, I don’t think, but I am coping. I am trying to get rid of the demons,” Herndon told the Record-Courier.

During the race, Herndon wore the names of the three who lost their lives in the Afghanistan IED blast on the his shoes, according to a Facebook photo.

According to race statistics, Herndon completed the Boston Marathon in three hours and 38 minutes and finished 11,334 overall.

“There’s a reason why I’m here,” he told the Post. “I’m just trying to find out what that reason is for.”