Tactical officers who shot and killed a gunman in the lobby of the Discovery Communications headquarters were prepared for the possibility that the bomb strapped to the man's chest would explode, a police commander said Tuesday.

Bomb technicians later determined that the device carried by James Jae Lee — which included a pipe bomb, four propane tanks and an oxygen tank — would have killed people nearby had it blown up, Montgomery County Assistant Police Chief Wayne Jerman said.

Lee was carrying a switch intended to detonate the bomb if he let go, but it didn't explode when he fell to the ground with fatal gunshot wounds and investigators aren't entirely sure why. At the time, SWAT team members had no idea what would happen, Jerman said.

"That was one of the big unknowns," he said. "They had to operate under the premise that with the dead man switch, it was going to cause or create some sort of explosion."

Lee, 43, took two Discovery employees and a security guard hostage on Sept. 1, the culmination of a yearslong crusade against the company and its networks, which he faulted in fanatical Web posts for offering programming that promoted overpopulation.

Jerman detailed the department's response to the hostage situation as part of a seminar on workplace violence prevention.

In a situation where deadly force is necessary, tactical officers prefer to have a sniper fire the fatal shot, but that wasn't an option in the Discovery case because the thick glass of the lobby windows would have altered the trajectory of the bullet, Jerman said.

Given that, there was no choice but for officers inside the building to confront Lee. Two teams of eight officers each were positioned out of sight in the lobby, and they moved in as soon as the two civilian hostages, Jim McNulty and Christopher Wood, ran out the front door. The attack was precisely choreographed, and the officers didn't hesitate despite the danger posed by the bomb, Jerman said.

"You want to neutralize the threat," he said. He did not disclose how many shots were fired and said he wasn't exactly sure how far away from Lee the officers were.

Jerman's presentation included recordings of Lee's conversations with a negotiator and chilling security-camera footage of Lee pointing starter pistols at the hostages. McNulty and Wood told The Associated Press in September that they concluded Lee had no intention of leaving the building alive, and Lee's comments to the negotiator make that clear.

"I have nothing else to live for," he told the negotiator. Asked what he meant, Lee said, "This is it. This is the end, all right?"

Although Lee had previously lived in homeless shelters, police discovered that he had been renting a room in the Wheaton area and searched his home the day after the hostage crisis, Jerman said. They found a calendar on his computer with Sept. 1 marked as "The End."

Jerman also showed videos found on Lee's computer in which he can be seen detonating a pipe bomb in a wooded area.

More than 150 county police officers, along with dozens from other agencies, responded to the Discovery crisis. An off-duty officer was one of the first on the scene and spotted Lee in the lobby. He found another entrance to the massive building, and that's how SWAT teams and other officers got inside, Jerman said.

Officers secured the control room for Discovery's network of security cameras and communicated what they saw to commanders outside, Jerman said. Employees were evacuated safely, and Lee wasn't able to go anywhere else in the building, he said.

The Columbine school massacre in 1999 changed the department's thinking on how to respond to a shooter inside an occupied building, Jerman said. Montgomery and other departments began training quick-response teams to get inside and take out the shooter instead of securing the perimeter first.

Jerman praised Discovery for having a detailed evacuation plan in place. Within an hour of Lee's arrival, he said, Discovery staff gave police a thick file on Lee, who had been convicted of disorderly conduct after a previous protest. He was ordered to stay away from the building as part of his probation, which ended in August.

Police would have preferred to take Lee into custody, but that didn't seem possible, Jerman said.

"In any operation like this," he said, "the ultimate resolution is no loss of life."