The main mass of runners had already passed, and we were already at home when news of the explosions broke. On the news, we saw the volunteers break through the barriers to help the injured, but no one dreamed it was a bombing. That doesn't happen in Boston. (We had old infrastructure trouble in the area which has blown covers off man-holes before when it catches fire. It wouldn't be too unusual.) What bothers me is that they took a beautiful, joyful day, sucked the feeling dry and replaced it with fear. It is a day for triumph, not terror.
(As an aside, the "third bomb" at the JFK library was the old infrastructure issue - just a transformer fire, not an attack.)
http://www.bbc.co.uk/news/world-us-canada-22160826