The Washington Post describes how social media have become "regular parts of the news ecology, serving as an early alert system":
The news of a gunman at the Discovery Channel's headquarters in Silver Spring indeed traveled fast on Wednesday, but none of it came through radio, TV or newspaper Web sites, at least not at first. As it has with other breaking news events—the landing of a jet on the Hudson River in 2009, the 2008 massacre in Mumbai—the story unfolded first in hiccupping fits and starts on Twitter, the much-hyped micro-blogging service that has turned millions of people into worldwide gossips, opinion-mongers and amateur news reporters.
Before camera crews and reporters could race to the scene, a shot of alleged hostage-taker James Lee was flashing around the world via Twitpic, Twitter's photo-sharing service that lets people see whatever a cellphone camera captures seconds after the shutter snaps. The shot—full of menace and dread—was apparently taken by an office worker peering from a window several floors above the Discovery courtyard. The photo was apparently passed from an unidentified Discovery employee to another, who posted it on Twitpic.
Another dramatic photo, of Montgomery County SWAT team members clinging to the sides of an armored vehicle as it rushed to the scene, soon followed, along with another, taken from the TV One building across the street, of emergency responders unloading a bomb-detecting robot on a street in Silver Spring.