The news broke around 1 p.m. with a few sketchy details. Gunman. Shots. Hostages. Discovery building.

Within minutes, there were photos, including an astonishing one of a man clad in shorts, carrying a rifle and stalking through what looked like an office courtyard.

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.

There was poignancy, too, as helpless friends, sympathetic strangers and relatives ("Please pray for my cousin . . . " read one) tweeted their fears and concerns to a communal thread, or hashtag, called #discovery. Others used the thread to signal the all clear: "Thank you everyone for your well wishes," read one, posted around 2 p.m. "@Discovery_News team all safe."

There were noteworthy documents linked in the massive tweet stream, too: a rambling manifesto of demands by Lee, his MySpace page and a YouTube video of Lee allegedly throwing money into the air on a busy street a few blocks from the Discovery building, in 2008.

TV can offer live pictures of an event (and local stations were on the scene quickly on Wednesday), and newspapers can provide context and fact-checking, but for raw speed and real-time eyewitness accounts, it's now virtually impossible for the mainstream media to keep pace with the likes of Twitter. The service enables anyone equipped with a smartphone to tell the world what he or she sees in 140-character bursts. Twitpic (as well as similar sites) can let them see it.

As it often does, the Twitter stream alerted the news media to the unfolding crisis. By around 1:30 p.m., mainstream news organizations, including The Washington Post, were adding brief news tidbits on their Web sites and sending out e-mail and Twitter alerts of their own.

News executives say social media sources such as Twitter and Facebook are now regular parts of the news ecology, serving as an early alert system. "It's a valuable resource that no news organization can afford to ignore," says Jim Farley, the vice president of news at WTOP, the all-news radio station. Although the stream of postings and tweets can be chaotic, he says, "there are far more people out there [reporting via social media] than any news organization could ever employ. They can tell you the size and shape of an event, and the right questions to start asking."

Among other uses, Twitter is an effective tool for finding personal stories in the midst of massive news events, such as last winter's snowstorms and this summer's earthquake in Montgomery County, Farley said.

But as rich as Wednesday's Twitter feed was, it was merely a starting point for reporters. "The initial information may have come to us through these tools, but we have to apply the old-media skills of vetting and serving as a filter" for what's accurate, said Allan Horlick, president and general manager of WUSA-TV. "We can't let raw info to go out over air. The front end is new, but we still have to do our work on the back end."