In the meantime, in the midst of death and injury and fear, come finish-line survival stories.
There was the 78-year-old man from Washington state who was knocked down by the explosion then got up and walked across the finish line and on to his hotel.
There was the 65-year-old woman from California who approached the end of the race just as the bombs went off and finished anyway. She was the 17,112th runner to cross the finish line.
Another 468 crossed it behind her.
Were the last finishers brave or just addled by exhaustion? Going forward by competitive reflex or because moving straight ahead seemed the best way out?
Whatever the explanation, they made it, and there is consolation in that fact.
By the standards of history and the world, we still live in an unusually safe place and time. That's hard to believe on days like Monday, and in an era when the worst of what human beings do to each other is instantly seen around the globe. And it doesn't diminish the cowardice and cruelty of Monday's attacks.
But in violating the hope of the finish line, the bombers may have given it new symbolic power.
A finish line is where ordinary people summon strength they couldn't have been sure they had.
One more time, that's what we're all called upon to do.