James Lee was no stranger to employees at Discovery Communications. In 2008, he staged a protest and wrote a lengthy online manifesto accusing the company of not doing enough to save the world.

On Wednesday, Lee’s protest turned violent. Police say Lee, armed with a gun and possibly carrying explosives, entered the company’s Silver Spring, Md., headquarters and took three hostages. After an intense four-hour standoff with police, Lee, 43, was shot and killed. The hostages were released unharmed.

Late Wednesday authorities were sweeping Discovery’s entire headquarters building to make sure it was safe for re-entry. Montgomery County police chief Thomas Manger said explosives teams were investigating four devices — two boxes and two backpacks — they believe Lee may have left behind in the lobby.

Nonetheless, execs said Discovery planned to reopen for business today.

“This is a scary event,” David Leavy, Discovery’s exec VP of global communications and corporate affairs, told reporters Wednesday. “We hope that we can get back to work tomorrow, but it is an active crime scene, and we’ll take our lead from law enforcement.”

Discovery staffers were asked not to speak to the media; Leavy said the company wanted “to be cautious and prudent in the statement that we make. The priority will be nurturing and responding to employee needs over the coming days.”

Discovery, Leavy said, “was familiar with this gentleman.”

“I don’t want to characterize the motivations of the perpetrator, but if you follow his writings online, I don’t think it was rational,” Leavy said. “We did not take his writings or demands seriously.”

In his online protest, Lee said about Discovery: “They aren’t even attempting to save the planet in my opinion….They are monsters and practically arms dealers.”

At one point, Lee got into a back-and-forth online battle with detractors, two of whom later identified themselves as Discovery staffers.

When his protest failed to attract followers, Lee began paying homeless people to show up at Discovery HQ. And when that fell short, he tossed thousands of dollars outside the company — attracting a mob scene. That action prompted police to take Lee into custody.

According to Manger, Lee spent two weeks in jail and was later barred from coming within 500 feet of Discovery offices. That prohibition expired two weeks ago.

Police said Lee entered Discovery’s lobby at about 1 p.m. ET on Wednesday, wearing metallic canister devices and holding a gun. He told everyone to stay still; some managed to escape, but Lee wound up holding three people — including an unarmed Discovery security guard — hostage.

In an odd twist, when an NBC News producer called Discovery, Lee picked up the phone.

“I have a gun and I have a bomb. I have several bombs strapped to my body ready to go off,” he told NBC, which played portions of the producer’s 10-minute conversation on “NBC Nightly News.”

Negotiators spent several hours talking to Lee. According to Manger, when it appeared that Lee was pointing a gun at one of the hostages, tactical units moved in and shot the suspect. At one point, one of Lee’s devices detonated, but Manger said it didn’t cause much damage.

Leavy credited Montgomery County police and fire officials, as well as the FBI and Discovery staffers, with handling the situation properly.

“We’re relieved it ended without any harm to our employees,” he said. “All of our employees are accounted for. We executed our emergency evacuation plan flawlessly. Everyone is safe and sound and we’re thankful for that… Our hope and expectation is tomorrow we’ll be back open for business.”