A gunman today took a small number of hostages at the headquarters of the Discovery Channel in Silver Spring, Md., a suburb of Washington, D.C. Police say he was carrying what might be an explosive device. The suspect has mounted protests over the years at Discovery regarding some of its programming. He is described by police as an Asian male.

Update 6:04 p.m. ET: Police shot Lee at 4:48 p.m. ET after he pulled out a handgun and pointed it at one of the hostages.

Lee's probation ended two weeks ago for his conviction for disorderly conduct and littering as a result of a February 2008 protest outside Discovery, police say. He had been ordered to stay 500 feet away from the building for the past two years. Lee paid homeless people to join him in his demonstration.

Police are sweeping the building for other possible explosives. Discovery officials plan to reopen tomorrow as usual.

Update at 5:52 p.m. ET: Police confirm the gunman was killed.

Police believe he brought two boxes and backpacks into the building that may have contained explosives.

All three hostages were men.

Update at 5:37 p.m. ET: Citing sources, the Washington Post is also reporting that the gunman is dead.

Lee was carrying indentification linking him with two local social service programs for the homeless.

Update at 5:29 p.m. ET: CBS News is reporting the gunman, 43-year-old James Lee, is dead. No confirmation from police.

Update at 5:17 p.m. ET: Montgomery County Police Chief Thomas Manger says police took action because "We believed the hostages lives were in danger," USA TODAY's Donna Leinwand reports.

Manger said an explosive device may have detonated after Lee was shot and fell. He said there was a "pop" and smoke.

Police are checking to see if the suspect brought other devices into the building.

Update at 5:03 p.m. ET: The suspect, identified as James J. Lee, has been shot by police and three hostages have escaped safely, police say. His condition is not known.

He was wearing backpacks containing what appeared to be explosives.

Lee has a history of protesting Discovery's programming, saying it has little to do with saving the planet. He was arrested outside the building in February 2008 after throwing thousands of dollars in the air.

At the time, Lee was identified as being from San Diego, listing his address as a local homeless shelter.

At his trial, he said he began working to save the planet after being laid off from his job in San Diego. He said he was inspired by Ishmael, a novel by environmentalist Daniel Quinn and by former Vice President Al Gore's documentary An Inconvenient Truth.

Lee was behind SaveThePlanetProtest.com, Montgomery County police and a Discovery official said.

Update at 3:23 p.m. ET: A law enforcement official speaking to the AP on condition of anonymity because the investigation is ongoing identified James J. Lee as the likely suspect. Police believe he has a handgun but have not confirmed that he has explosives, the official told the news agency.

The Washington-area news site DCist reported in 2008 that a man identified as James Jay Lee was the organizer of a lengthy protest against The Discovery Channel, and had been arrested by Montgomery County police. WJLA reported that Lee was arrested on charges of littering and disorderly conduct, apparently for literally thrown money at people on the street so that they would gather around his protest site.

Earlier posting: The Discovery Channel building in Silver Spring, Md., has been evacuated because of reports of an armed man on the premises, CNN reports.

Update at 1:35 p.m. ET: WJLA reports that Montgomery County authorities confirmed the report and say that at least one shot was fired by the gunman.

Update at 1:37 p.m. ET: WJLA says witnesses heard "five or six" shots.

Update at 1:38 p.m. ET: WJLA says the suspect was carrying a shiny revolver and was carrying "tanks" on his back.

Update at 1:40 p.m. ET: Montgomery Co. Cpl. Dan Friz tells WJLA that the suspect was carrying what appeared to be an "explosive device."

Update at 1:57 p.m. ET: WUSA reports that the gunman is believed to be holding at least one hostage.

Update at 2:24 pm. ET: The Associated Press quotes Maryland police as saying the gunman has taken at least one person hostage.

Update at 2:31 p.m. ET: The gunman is an "Asian male" whose "concerns" are with the Discovery Corp., according to Montgomery County police spokesman Dan Fritz, who would not elaborate on any possible motive. Friz says authorities are speaking to the suspect. Friz also says that the suspect is carrying what some officials believe may be an explosive device. (Correction: this police spokesman is now identified as Capt. Paul Starks, not Fritz. )

Update at 2:53 p.m. ET: NBC News is reporting the name of a suspect in the hostage-taking. We have not been able to confirm the name, but a person using that name was reported by a local DC news site in 2008 as having been arrested for protesting Discovery's Save the Planet and Planet Green programs. The news site says the man was arrested for reportedly throwing money at people on the street in front of the Discovery building.

Update at 3:07 p.m. ET: Montgomery County fire department spokesman Capt. Oscar Garcia said three bomb technicians responded to the scene and several more were on their way, the AP reports.

Update at 3:11 p.m. ET: USA TODAY's Donna Leinwand sreports that workers were told after the incident began to move into lockable offices and to turn off the lights. Jennifer Manvilla, 28, a royalty and contracts management specialist at Discovery's finance division, said she was working on the 5th floor when other employees came through office with instructions on where to take cover.

Update at 3:18 p.m. ET: Montgomery County police chief Tom Manger tells reportrs that the gunman has a "small number of hostages." He also says that police "are in negotiations with him."

(Posted by Doug Stanglin)