Here's a livestream from the scene:
Here's a link to the Boston Police, Fire and EMS Live Audio Feed.
UPDATE: This are the first two videos we've seen that show the actual explosion as it occurred. It's graphic.
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Top photo via @Boston_to_a_T
Amazing photo of Boston's first responders:
Police react in aftermath of explosion #bostonmarathon #boylstonst (John Tlumacki photo) twitter.com/BGlobeSports/s…
— Boston Globe Sports (@BGlobeSports) April 15, 2013
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