"I crossed the finish line at 4:06 (hours on the course) and it happened at 4:09, right behind me," the 49-year-old Muro recounted of the bombings that injected death and destruction into the annual highlight of Patriot's Day celebrations in New England's biggest city.
Ironically, she was grateful her pace had not been faster. "If I didn't pick it up at the end, I potentially could have been right in front of it."
"It was very surreal," Muro said, "because it was only two blocks in back of me. If I had been just a little bit slower, I would have been right in the spot.
"I was just there," she said. "It was one of those things where you feel like you dodged a bullet."
The back-to-back explosions shortly before 3 p.m. at the finish line of the 117th marathon, which attracts thousands of runners -- including 15 from Westport this year -- caused at least three deaths and nearly 150 injuries, many of them traumatic. By then, according to race officials, about three-quarters of the 23,000 runners who turned out for the marathon had completed the event
"I crossed the finish line," Muro recounted. "I stopped my watch and I was in the post-race area ... where they give you the medals.
"As I was walking through, you heard this loud explosion, almost like a building imploding, because the ground shook," Muro said. "And then when we looked back, we could see a 50-foot plume of smoke, like a vertical plume, rising."
A few seconds later, she said, another explosion occurred. "The runners were kind of looking at each other, like, `This is obviously not a good thing.' "
Another marathon runner from Westport, Blake Benke, who served five years in the Marine Corps, knows a bomb explosion when he hears one.
And that experience proved of value Monday.
"I could just feel the buildings reverberating. My wife was like, `Maybe a water main broke.' I said, `Diane, that's not a water main, that's a blast. We need to get off the streets," said Benke, who was about a block from the bombings at the Boston Marathon.
Monday's race was Benke's 11th marathon. He had finished in under three hours -- 516th overall -- and returned to his hotel for a shower and was heading out with his wife for a post-run drink when the attacks occurred.
Speaking by phone from the hotel room, Benke said later the perpetrators knew how to strike a nerve.
"You run on Patriots' Day (a Massachusetts holiday). There's nothing more pure than the Boston Marathon," he said.
Of the 15 Westport runners registered to run in the marathon, according to the reace website, 10 completed the course.
Muro, who drove to Boston for the marathon with her husband Jon, their 16-year old daughter Emma and her parents, finished the 26.2-mile marathon course in the position of 16,848th overall, and 6,572nd among women. As a veteran of 14 marathons, she said she might have finished faster but chose to stop along the route to visit with family.
The second explosion occurred seconds after the first, she recalled later Monday.
"I heard a second explosion," she said. "I couldn't really see any smoke, but you knew it was significant because, again, it was very loud. It had a vibration to it."
"We proceeded to walk away from the finish line and I went to the bag line and I overheard somebody saying they heard they suspected there was a third bomb," she said.
That's when Muro sent a text message to her husband and daughter, who had waited at Mile 22 on the race course, and planned to meet her at the finish line.
"I said, `Don't come down here. You don't want to come down here. Two bombs went off,' " she said.
Muro managed to grab her bag from the school bus that had transported her to the race starting line at the beginning of the day.
"I was able to get my bag," she said. "All of a sudden the police came down. They cordoned off the area. They blocked the finish line."
Officials also prevented all later runners from retrieving their belongings, as police suspected other explosives could be planted elsewhere in the area.
"My understanding is that a lot of the runners ... were not able to get their bags, because once they discovered there was potentially undetonated bombs, they closed the area down," she said.
Her family, meanwhile, had to walk back to their hotel since Boston Metro's T-line was closed down outside that nearby station.
"You never even think about something like that happening in an event like this," Muro said of the attacks.
Another runner from Westport, Jeffrey Clachko, 40, posted on his Facebook page: "Thanks for everyone's concern." he said in a Facebook posting.
"I was 10 seconds in front of the explosion ... awful awful awful. Trying to meet up with Betsy and the boys now."
A Fairfield native running in the marathon initially thought the emergency-services personnel rushing by her as she and hundreds of other runners approached the downtown finish line Monday afternoon were dispatched to an accident or medical emergency at the end of the 26.2-mile course.
"Every so often you'd have to move to the right because either a police car or an SUV or fire engine was going through," said Julia Daly, who grew up in Fairfield and now lives in Cambridge, Mass. "I just thought that maybe someone had a heart attack or medical emergency ... It never dawned on me that anything like that had happened."
Daly was about six miles from the marathon when she first noticed the growing deployment of emergency vehicles and sidewalks empty of spectators along the route.
A woman running alongside told Daly about explosions at the finish line.
Daly used the woman's cellphone to text her family farther down the route to make sure they were safe, including her father, Fairfield resident Michael J. Daly, the editor of the Connecticut Post editorial pages.
"Everyone's rooting for the people who were running and it's this very positive kind of thing (and) then all of a sudden I saw these military guys running," Michael Daly recounted. "It got very quiet. Suddenly there were sirens, there were helicopters circling over head.
"It went from a very festive thing to a very bizarre thing," he said.
Norwalk resident Jim Gerweck, editor-at-large for Running Times magazine, was in the marathon press room at the time of the explosions.
"As soon as the explosions went off, or within minutes after that, we were put in lock down," he said. "Almost every building in the area was. They wouldn't let anyone out, so we were in that situation for almost five hours, so I didn't see anything more than what anyone saw on TV really."
Gerweck and other reporters, however, heard and felt the explosions.
"We could hear and even kind of feel it," he said. At first he thought the blasts might be thunder, but "given the (weather) conditions, that wasn't likely."
"I was thinking it could have been some sort of a building collapse, but it didn't take long before we were told it was an explosion," he said. "There was a lot of speculation that it could have been a gas line or something like that."