At least three people were killed and more than 130 injured from two bombs that exploded near the finish line of the race, held on Patriots' Day. Growing up in the Boston area and during his tenure with the Red Sox, Epstein often watched the race, which coincides with a morning Red Sox game.
"My mom used to run the marathon, she probably ran a half-dozen times, and her twin sister," Epstein said Tuesday. "There are a lot of memories of going to see them run by, going to a few Red Sox games, Patriots' Day games, and for a decade, going to work and seeing the game. I'd always leave the game at about the seventh inning to go see my brother run by and kind of pull the hat down, hand out, give him a high five, and then go back to work."
In response to the bombings, the Cubs increased security at Wrigley Field prior to Tuesday night's Interleague game against the Rangers.
"Everyone who works in sports has a responsibility to be extremely vigilant," said Epstein. "We have large crowds on a nightly basis. They trust us with their safety, and obviously it's difficult to keep large numbers of people safe. You have to take every precaution.
"We take a lot of precaution on a regular basis, but we ramped up security even tighter today in the aftermath of what happened yesterday and will continue to do so. People in sports have an added obligation."
Cubs general manager Jed Hoyer, who also lived in Boston while working for the Red Sox, said watching the explosions on television was "horrific."
"The injuries and the loss of life is awful," Hoyer said. "If you live in Boston for any amount of time ... [Patriots' Day] is kind of the best day in the city. The Red Sox game is in the morning, everyone has off work, everyone runs out of the Red Sox game and goes right to the race and watches the end of the race, and there's usually tons of parties and gatherings at night. It's a day that's unique to Boston and unique to Massachusetts and everyone has a great time and lives it up. For the rest of the country, most cities don't have that one holiday that's unique to them."
Epstein said he used to live about a block south of the finish line on Boylston Street, where the first explosion occurred, and he has walked down that street thousands of times. Anyone who visits Boston has probably walked down Boylston.
"All my thoughts are with my hometown and the people of Boston," Epstein said. "It's a horrific thing that happened. it's surreal that it happened in the middle of the city. The city is really shaken, but it's an extremely resilient city with lots of tough people. They'll definitely get through it.
"It's almost impossible to process something like that, on such a special day in Boston, too. The thing about the marathon, just about everyone there was waiting for a loved one or friend or to cheer on a stranger, and to have someone try to kill and hurt strangers, it doesn't make sense. It's amazing that human beings are capable of both those extremes -- there to support strangers and there to hurt strangers. It's a shocking event, tragic event, but I know Boston's tough enough to get through it."
Hoyer also felt Boston would rebound from the tragedy. The images will be hard to forget.
"Seeing the blood on the ground outside buildings that you'd walk past every day is hard," Hoyer said.