Here's video someone took from their live TV screen of the actual explosion:
What kind of message does a terrorist intend to send by bombing a sporting event!? I can sort of understand the implied meaning of slamming planes into the WTC but when the topic of bombing the olympics comes up... and of today's atrocious events I just find myself grasping to understand the underlying meaning. Maybe Boston's security was weak? I can't fathom that since the USA seems pretty competent these days about having lots of officers and security on the ground at these kinds of events. Perplexing, gruesome and disappointing.