Maryland State Police troopers surround the Discovery Channel network building in Silver Spring, Md., Wednesday. Police later shot and killed a man who had taken two employees and a security officer hostage.

SILVER SPRING, Md. — A gunman police shot to death after he took hostages at Discovery Channel's headquarters said he hated the company's shows such as "Kate Plus 8" because they promote population growth and its environmental programming because it did little to save the planet.

Three hostages — two Discovery Communications employees and a security guard — escaped unhurt after the four-hour standoff Wednesday in Silver Spring, just outside the nation's capital. After several hours negotiating with the gunman, tactical officers moved in when authorities monitoring him on building security cameras saw him pull out a handgun and point it at a hostage, said Montgomery County Police Chief Thomas Manger.

A source identified James J. Lee as the suspect, but police had not released the gunman's identity.

It wasn't the first time Lee, a homeless former Californian, had targeted Discovery's headquarters. In February 2008, he was charged with disorderly conduct for staging a "Save the Planet Protest." In court and online, he had demanded an end to Discovery Communications shows such as TLC's "Kate Plus 8" and "19 Kids and Counting."

Instead, he said, the network should air "programs encouraging human sterilization and infertility."

"Humans are the most destructive, filthy, pollutive creatures around and are wrecking what's left of the planet with their false morals and breeding cultures," Lee wrote in a bitter manifesto on his website.

Lee, 43, also objected to Discovery's environmental programming. He wrote in 2008 that a show he called "Planet Green" was "about more PRODUCTS to make MONEY, not actual solutions."

Police say the gunman burst into the building about 1 p.m. and took hostages in the lobby on the first floor. An explosive device on his body detonated when police shot him, Manger said. Authorities later sent in a robot to disarm a device on the gunman's body.

Manger said the gunman had four explosive devices strapped to him. He described two of them as propane cylinders with pipes attached that contained shotgun shells. Manger said the other two were pipe bombs.

None of the 1,900 people who work in the building were hurt, and most made it out before the standoff ended Wednesday.