Boston Police Superintendent William Evans walks down the chute at the finish of the Boston Athletic Association half marathon in Boston. Evans has run the Boston Marathon 18 times, and finished in 2013 before the bombings occurred. This time he will be there as police commissioner, supervising increased security. "It weighs heavy on my mind, that I want this to go off well," he says. "I don’t want anyone hurt. I don’t ever want a repeat of the tragedy we saw that day."