Police have shot and killed a gunman who spent Wednesday afternoon holding three hostages in the lobby of the Discovery Communications Building in Downtown Silver Spring, Maryland.

James Jay Lee, a man with a history of mental illness and environmental extremism targeting the Discovery Channel, entered the building at One Discovery Place at approximately 1 PM and took over the facility with the help of a gun and devices resembling pipe bombs.

Montgomery County Police Chief Tom Manger said officers shot the gunman at about 4:50 p.m. because law enforcement “believed the hostages were in danger” after hours of negotiations.

“We had been talking to him for several hours and he had a wide range of emotions.”<

Lee’s three hostages escaped unharmed and police are checking the building for other possible explosives.

Two years ago, Lee was arrested for littering and disorderly conduct at the Discovery headquarters. Lee, 43, organized the 2008 protest to decry what he perceived to be irresponsible editorial and environmental attitudes at Discovery. He advertised his campaign online and in publications, including The Washington Post’s free daily paper Express. The environmentalist — with ties to a wealthy Washington family — also hired homeless people in the area to increase the numbers of people at his protest.