BOSTON -- Sung Ho Choi of Jacksonville ran in his 10th Boston Marathon on Monday.

He came in at 3 hours, around 1:20 p.m., then returned to his hotel. He heard the bombs going off while he was in the shower.

"When I went into the shower, and had the water running," he said. "that's when the bombs went off. I was in total shock. I was just like ... I didn't know what to think."

Choi, who goes by Henry, said he was in shock.

"I didn't expect anything like this to happen at a running event," Choi said. "This was a heinous and cowardly act. Given what we know know about what took place, the FBI is investigating it as an act of terrorism."

He said it shows the need for vigilance, no matter where you are.

"You just gotta keep an eye out on everybody and you just gotta be careful."

Even after the devastation of the bombings, Choi said he will keep running.

"This is not going to stop me at all."