As the three hostages at Discovery Channel's headquarters appeared ready to make a run for it, police said Thursday that a SWAT team officer quickly shot and killed the increasingly agitated gunman who had explosives strapped to himself, ending the four-hour standoff.

After several hours of negotiations, the tactical officers moved in. Authorities saw the hostages begin to move on building security cameras and heard a "pop" they believed to be a gunshot or an explosive device, Montgomery County Police Chief Thomas Manger said. That's when an officer shot the gunman, James J. Lee, in the lobby of the building in Silver Spring, just outside the nation's capital. None of the hostages were hurt.

"For most of the time, the hostages were laying on the ground, and he didn't engage them much other than saying on the phone, 'I don't care about these people,'" Manger said.

Lee had said he hated the company's shows such as "Kate Plus 8," claiming they promoted population growth. Lee said the environmental programming did little to save the planet.

Manger said police planned to negotiate as long as necessary, but acted when officers believed the hostages were trying to escape.

"We saw some hand movements from hostages," Manger said. "We're watching this and trying to keep the focus of the guy we're talking to. We didn't know if they were up to something or what they were doing. We are surmising they were making a break for it."

Manger called the hostages and the officers heroes.

Lee repeatedly said he was "ready to die," the police chief said.

"I believe he was not intending to come out of there alive," Manger said.

It wasn't the first time Lee, a homeless man who previously lived in Californian, had targeted Discovery's headquarters. In February 2008, he was charged with disorderly conduct for staging a "Save the Planet Protest." Lee threw fistfuls of cash in the air and paid homeless people to carry signs condemning the network. Police found his pockets stuffed with more than $20,000, according to court records.

Lee served two weeks in jail after his arrest during which doctors evaluated his competency to stand trial. County State's Attorney John McCarthy said Lee was ordered to stay 500 feet away from Discovery headquarters as part of his probation, which ended two weeks ago.

In court and on his website, he had demanded an end to Discovery Communications LLC's shows such as TLC's "Kate Plus 8" and "19 Kids and Counting." 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 said he burst into the building about 1 p.m. and took hostages in the lobby. He had four crude explosive devices strapped to him. Two of them were green propane cylinders with pipes attached that contained shotgun shells. The other two were pipe bombs.

One of the devices detonated when police shot him, Manger said. Authorities later sent in a robot to disarm a device on the gunman's body.

Lee also had what appeared to be a remote radio frequency or a remote switch with an antenna on it, and police were concerned Lee could use a remote control to set off bombs. Police also discovered batteries, two handguns and two ski masks at the scene.

NBC News reported that after its producers called Discovery's general number, a man identifying himself as Lee got on the phone and said he had a gun and several bombs.

"I have several bombs strapped to my body ready to go off. I have a device that if I drop it, if I drop it, it will ... explode," the man told NBC.

He said he built the bombs in about three weeks. "I did a lot of research. I had to experiment," he said.

One hostage, Discovery employee Jim McNulty, posted a message on the company's website, thanking authorities for "helping to ensure the safety of all my colleagues" and "for helping to get me and my fellow hostages out safely." He said he wouldn't talk now about what happened because police were still investigating.

Lee faulted the Discovery Channel for shows as varied as "Future Weapons," "It Takes a Thief" and "Planet Green." Instead, he sought programming based on "My Ishmael," a book by philosopher Daniel Quinn in which a telepathic gorilla instructs a 12-year-old girl on society's failings. On his MySpace page, Lee said his heroes were Quinn and "Star Trek" commander James T. Kirk.

Quinn said in an interview from his Houston home that Lee misinterpreted his book's message about the folly of continually increasing food production to meet population demands.

The author said he hadn't heard of Lee before Wednesday but called his death "pretty horrible." Had he been able to speak with him, he would have told Lee "he's giving a bad name to the ideas that he's trying to espouse."

Lee in 2008 also held a related contest promising $200,000 worth of Hawaiian real estate for the best essay proposing a save-the-planet TV show. On his MySpace page that has since been taken down, he lists his home as Hawaii.

The Maui News and KHON-TV reported that Lee had lived in the Lahaina area of West Maui. The newspaper reported that he was a 1985 graduate of Lahainaluna High School and his former classmates and principal described him as a normal person who didn't cause any trouble.

"As far as I'm concerned, he was a good kid," former Lahainaluna principal Henry Ariyoshi told The Maui News.

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

"We're relieved that it ended without any harm to our employees," said David Leavy, Discovery's executive vice president for corporate affairs.

The building was to reopen briefly Thursday for employees to return. Counselors were offering assistance to Discovery Channel employees, said Catherine Frymark a company spokeswoman.

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Online:

Lee's website: http://www.savetheplanetprotest.com

http://corporate.discovery.com

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Dishneau reported from Hagerstown, Md. Associated Press Writer Kathleen Miller and Associated Press Photographer Jacquelyn Martin in Silver Spring; Matthew Barakat in Rockville, Md.; Matt Apuzzo, Adam Goldman, Eileen Sullivan and Nafeesa Syeed in Washington; Ben Nuckols in Baltimore; Ramit Plushnick-Masti in Houston, and Jacob Jordan in Atlanta contributed to this report.