Here are the stories we're looking at this morning
Boston on high alert after marathon bombing kills 3, injures scores
Boston blast injuries required battlefield savvy, experts say
Kevin Cullen: A perfect Marathon day, then the unimaginable
E.J. Dionne: Patriots’ Day defiled
Scott Lehigh: A tough blow -- but a tougher town
Washington Post: In Boston, explosions transform a scene of celebration into one of tragedy
NYT editorial: Bombs at the Boston Marathon
The Boston Marathon's Final Mile Was Dedicated to Newtown Victims
Brothers watching Boston Marathon each lose a leg
Hospitals treat carnage after blasts