The hostages were not injured. At least one explosive device went off when he was shot.
The armed man, James J. Lee, walked into the lobby of the Discovery Communications building around 1 p.m. EST, armed with a pistol and a device strapped to his body that police treated as potentially explosive.
Some 1,900 employees were evacuated during the incident. No Discovery Communications employees were injured.
Police said Lee had ongoing issues with Discovery over its environmental lineup during the last several years. A longtime protester at the building, Lee was sentenced to six months of supervised probation for disorderly conduct in March 2008.
Various radical environmental statements have been attributed to Lee via a Web site registered to him, including his desire to air programming on Discovery's various networks. It read:
"I want Discovery Communications to broadcast on their channels to the world their new program lineup, and I want proof they are doing so," he wrote. "I want the new shows started by asking the public for inventive solution ideas to save the planet and the remaining wildlife on it."