Bill Iffrig, 78, lies on the ground as police officers...

Bill Iffrig, 78, lies on the ground as police officers react to a second explosion at the finish line of the Boston Marathon. (April 15, 2013) Credit: AP

The Boston Marathon has forever been a rite of spring the nation watches and enjoys, and because of that, we all feel a personal sense of violation in what happened yesterday.

As New Yorkers and as Americans, we're profoundly angry at the violence unleashed in Boston on Patriots Day, the city's proudest day of the year.

We also know what Boston stands to lose as a community -- beyond the death toll and beyond the list of injured -- as a result of the explosions. All civilizations are built on trust, and Boston might lose a little of its customary public ease.

These moments demand extraordinary courage and resolve, and there's no doubt the people of Boston and the nation will answer the call. But it's infuriating and wearying that we must yet again bear such a heavy burden. An 8-year-old boy was among the dead, and scores of people who came to enjoy a wonderful sporting event were maimed and injured.

It wasn't clear yesterday who did this or what twisted statement they sought to make with such wanton disregard for human life. But with two devices exploding almost simultaneously within 50 to 100 yards of each other near the marathon finish line, and others that failed to detonate, it seems pretty clear this was a coordinated terrorist attack.

A somber President Barack Obama pledged yesterday that the people responsible will be found and brought to justice. That's imperative. Law enforcement and anti-terrorism officials have proved equal to the task many times in the past. They must again.

But that's not enough. With civilians targeted at such an iconic, high-profile event, international terrorism, of course, immediately comes to mind. If that's what this was, the more difficult job is to find the people who directed it and hold them accountable. If it proves instead to be the work of domestic terrorists, as was the 1995 bombing of the federal building in Oklahoma City, we have to figure out what in our culture breeds such violence and how to stop it.

It's important not to jump to conclusions. Officials said there was no advance threat to the marathon and no one immediately claimed responsibility. And with a race that garners international attention, run on Patriots Day, which this year was the last day for filing federal taxes, there is any number of possible motives for this madness. But with so many people, cameras and police concentrated in the area, authorities should be able to find those responsible for this latest assault on the American spirit.

In New York after 9/11, we entered a new world of wariness -- with omnipresent police patrols, security cameras, license-tag readers, bomb-sniffing dogs, metal detectors -- intrusions that have become numbingly routine.

At the same time, these painful tears in the civic fabric can also bring us together in odd ways. Old rivalries suddenly seem silly. Regional feuds seem beside the point. We are all Bostonians, New Yorkers, Washingtonians, Oklahoma City residents. We are all Americans, and we do what we can for each other.

The task now is to make sure the unthinkable doesn't happen yet again.

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