It was mentioned on the news last night that just about every federal agency has agents at Boston Airoprt interviewing departing passengers. They are asking if they took pictures or videos anywhere or at any time during the marathon. If so they ask to download those images before the passenger boards his/her plane. Now that is good thinking.
Update: No, Bruce, I'm not being sarcastic. The Federal Bureau of Ineptitude sometimes gets things right. Just as a stopped clock is right twice a day, they can't help it.