IN THE weeks and months after the 2001 terrorist attacks, every iconic sports event became an occasion for anxiety. World Series games, the Super Bowl — with each, trepidation suffused every fan’s normal interest.

Over time, the trepidation faded — until Monday. The Boston Marathon, held each Patriot’s Day, is about as iconic as a sporting event can be, for the world’s elite runners and for Bostonians, whether sedentary or fit. As Massachusetts Gov. Deval Patrick (D) said, “This is a pretty special day around here.” That it would be despoiled by two explosions near the finish line, killing at least three and injuring scores, is a terrible development.

In the early moments after the blasts, there were indications of the nation’s maturity, for better and worse, in dealing with such shocks. Runners and onlookers seemed to respond, for the most part, without panic. Local police began cooperating seamlessly with state police and the FBI and other federal authorities. Emergency crews responded with professionalism.

Officials and reporters, meanwhile, were careful not to get ahead of the confirmed news. Could the explosions have been something other than bombs? In the late afternoon, Boston Police Commissioner Ed Davis confirmed that they were explosive devices.

Who was responsible? Again, there seemed to be a general understanding of the danger of jumping to conclusions. The nation has seen its share of foreign terrorism and homegrown terrorism attacks alike (the 1996 Summer Games in Atlanta come to mind). Sadly, any number of explanatory scenarios were plausible, absent a claim of responsibility and pending a more thorough investigation.

Washingtonians who knew a marathoner, or whose friends or loved ones were in Boston for other reasons, frantically sought reassurance. For everyone else, there was little to do but hold the victims in their hearts and wait for more clarity. Unfortunately, we’ve learned well by now that “senseless” doesn’t mean “unlikely.” Even so, who could help but feel furious that anyone would target such a sunny event and so many innocent people?