"I still have those images in my mind, " said Dubner, 55, an actuary in Atlanta.

NPR: The Finish Line: What The Bombing Was Like

The Boston Marathon was also the 50th marathon for Jerry Dubner.

NPR: The Finish Line: What The Bombing Was Like

In their best seller Freakonomics, he and co-author Stephen Dubner note that a child is 100 times more likely to die in a swimming accident than a gun accident.

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