Explosions at the Boston Marathon. People killed, including a child; grisly injuries among runners and spectators.

• Photos of the carnage.
• Video of the blast as seen by a runner.
• Schneier recommends responding to terrorism with indomitable calm.
• How to Help.

May all affected find aid and comfort, and the bombers be brought to justice.

Update: Speaking of bringing the bombers to justice, a timeline of the hunt for the suspects, and profiles of the Tsarnaev brothers from NYTimes and Boston Globe.