Two explosions at the finish line of the Boston Marathon have killed 2 and injured more than 100, with reports constantly changing as new updates flood in.

As is now par for the course, news of the disaster broke first on Twitter, and the microblogging service remains an unparalleled source of breaking news and first-hand accounts — not to mention media criticism of news outlets that jumped ahead of the facts in their reporting.

The presumed attack has since been documented in thousands upon thousands of user generated images and videos  spread across the Web through social media channels. (Among other things, this Vine video appears to show one of the first explosions.) Spencer Ackerman over at called it a “live-tweeted disaster.”

Boston-area and federal authorities have also embraced Twitter to get out public-safety messages — for instance, asking people to stay away from the affected area and not to congregate in large groups. Police have also requested video from spectators: 

(Atlantic Wire’s Alexis Madrigal looks into how investigators might analyze contributed video.)

The Boston Globe received a video of the finish line during the initial explosion, embedded below. This video doesn’t contain any graphic images of injured individuals, but it does feature the explosions, the onset of immediate panic in the crowd and police and marathon volunteers rushing to assist victims.

Google has also just launched a person-finder web tool to help those trying to reach friends and family members.

Of course, any disaster aftermath has to feature its share of incomplete, misleading or just plain wrong reports. (It may take days to figure out which category some news reports fall into.) For instance, at 4:55pm, the Associated Press reported that officials had shut down cell service in Boston to prevent any further explosions:

Only, that is, to walk back the story about 45 minutes later:

Similarly, early reports that a third bombing took place at the JFK Memorial Library are apparently false. The library’s official Twitter feed reports that the incident was a fire that started in the mechanical room, and that all staff and visitors are accounted for and safe.

nick statt