But approximately four hours later, while sitting in his locked down hotel adjacent to Monday's fatal explosion, he conceded the event had turned into a nightmare. He said ATF agents were swarming the building while he and his wife, like the rest of the nation, attempted to glean what information they could from media reports.
"At first we didn't know what it was, but it sounded like a bomb could have went off," Horton said of the explosions, which as of late Monday had killed two and injured more than 100. "When we saw the people running we knew something had happened. People were crying, all the sirens started. Total chaos."
Horton, a mechanic for Wellmont Health Systems, completed his run in three hours and 50 minutes. He said that just as he and his wife were reuniting in a family meet-up area the explosions rocked downtown Boston.
"We were still outside when the blast occurred, probably about a block and a half from it," said Horton. "We heard both blasts. We were behind the hotel that divided us from the finish line. Especially after just running 26 miles, I was hobbling to the hotel about half sick. It was all quite traumatic."
"This has been my goal to qualify to run the Boston Marathon. All this puts a damper on it; people dying here."
The Boston Athletic Association's online entrant list for the marathon included two additional Kingsport residents; David Lively Jr., 43, and Brandon Raff, 29.
Lively's mother, Barbara Lively, told the Times-News that her son had finished the Boston Marathon prior to Monday's explosion, and was on the way back to his hotel when the incident occurred.
Attempts to reach Raff were unsuccessful, with other media outlets reporting he was OK.