Police in Silver Spring, Maryland said the man who took several people hostage at gunpoint at the headquarters of the Discovery Channel has been shot and killed by police and the hostages have been freed.

A law enforcement official identified the man as James Lee, who has protested in the past against the channel's environmental programming, saying it has done little to save the planet.

Authorities said Lee entered through the main entrance of the building around 1 p.m., wearing metallic devices strapped to his body and was waving a handgun.

Most of the 1,900 people who work in the building were able to get out safely.

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