James Lee had two propane tanks attached to shotgun shells as well as two pipe bombs that "contained fireworks-types explosive," Montgomery County Police Chief Thomas Manger told CBS' The Early Show.
As negotiations went nowhere, police were watching security cameras and saw Lee aim his gun.
"He pulled out the handgun he came in with and pointed it at one of the hostages," Manger said. "But at that point our tactical unit moved in and shot the suspect."
Manger said that after Lee was shot by police, their first priority was to make sure the hostages were safe and to disarm the explosive devices.
"It took about four hours for the bomb squad to render all of those devices safe," he said.
During the negotiations with Lee, police saw what appeared to be a switch in the suspect's hand, Manger said.
"It had a wire coming out of it, which may have indicated it was -- there was a radio switch to an explosive device," Manger said.
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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 LLC's 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.
Manger said that police were made aware of Lee's contentious history with Discovery Communications. "We were very quickly aware of who we were dealing with," he said.
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. A gun wasn't his only weapon, as an explosive device on his body detonated when police shot him, Manger said. Police were trying to determine whether two boxes and two backpacks the gunman had also contained explosives and authorities later sent in a robot to disarm a device on the gunman's body.
NBC News reported that after its producers called Discovery's general number, a man identifying himself as James J. 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.
Manger told The Early Show that the hostages remained "courageous" throughout the ordeal.
"We were on the phone with him for most of that time. He repeatedly said that he was ready to die," Manger said. "They certainly, hearing only his side of the conversation, had to just be terrified with what they were hearing."
Hours after the standoff ended, county police and firefighters looked at a laptop screen that showed a body face-up, surrounded by blood. It was unclear whether the body had been removed from the building Thursday morning. Police Capt. Paul Starks said the suspect had shot a gun at least once and that authorities believe he was acting alone but are investigating all possibilities.
Lee's mission against the Discovery Channel goes back at least a few years. In the February 2008 protest in which he was arrested, he 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.
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 hometown 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.
Melissa Shepard, 32, of Peterborough, N.H., a consultant who works in the building, said she was on the third floor when someone announced over a loudspeaker that there was a situation in the lobby and people should stay at their desks.
After some time, they were told to move to the other end of the building. She said she was among a dozen workers who went into an office, shut the door and turned off the lights.
Then she said someone knocked on the door and told them to leave the building. She said there was some confusion as they were told to go to an upper floor or down the stairs.
"Finally, I screamed, 'Tell us where we need to go! ... I just want to get out of there,"' she said. "I was shaking. ... I was like, 'What do we do? What do we do?"'
(Above: A man believed to be hostage-taking suspect James Lee is seen protesting the Discovery Channel in 2008.)