For years, state and local officials have conducted a "tabletop exercise" before the Boston Marathon, a meeting that allows them to study a map of the 26.2-mile course from Hopkinton to Boston's Copley Square and plan for emergencies that could arise during the race. A large crowd gathers to pose for photos at the Boston Marathon finish line, one day before the race, Sunday, April 20, 2014, in Boston. Runners and race fans crowd Boyslton Street at the Boston Marathon finish line, one day before the race, Sunday, April 20, 2014, in Boston. Wellesley College student Tiffany Liao, of San Marino, Calif., center, serves a pasta dish during a Boston Marathon pre-race dinner at Boston City Hall, Sunday, April 20, 2014, in Boston.