BALTIMORE — A security guard who called 911 after a gunman entered Discovery Channel’s headquarters calmly told the operator: “You’re probably going to need a sniper.”

The call, released Friday, was one of several placed minutes after a gunman entered the lobby and took three hostages. Other callers described the propane tanks strapped to the gunman’s body, and a blinking device in his left hand.

After hours of negotiating with James Lee, 43, police shot him to death as the hostages were preparing to make a break for it, police said.

Even in the first minutes after the siege began, Discovery security had an idea of who they were dealing with. A security employee told a 911 operator that they believed the man was in the lobby was Lee, who is originally from Maui. He told the operator Lee appeared disoriented, had propane tanks strapped to his chest and at least one person on the ground.

“It looks like he’s got an IED. He looks like he’s setting up an explosive device in the lobby, you’re probably going to need a sniper,” he tells the operator. “You gotta move fast.”

In police radio transmissions, an officer described the suspect as an “Asian male following the do-not-admit sign Discovery has.”

Lee, who was periodically homeless, was charged with disorderly conduct in February 2008 after he staged a “Save the Planet” protest outside the Discovery building. He threw fistfuls of cash in the air and paid homeless people to carry signs condemning the network. Police found him with a duffel bag stuffed with more than $20,000, according to court records.

He was convicted and served two weeks in jail and was ordered to stay 500 feet away from Discovery headquarters as part of his probation, which ended two weeks ago.

Radio transmissions detail the urgent attempts to evacuate the building and clear traffic and people from the streets around the Silver Spring building in the heart of the bustling downtown during lunchtime. One officer describes Lee setting up a bullhorn with a remote microphone.

Later, one of the police snipers described the explosive device Lee had strapped to his body as coffee cans and propane canisters. The officer said Lee had a microphone and was “protesting verbally.”

One Discovery employee told an operator that she was hiding in the kitchen of the building’s cafeteria with other employees. She said the man came in the lobby.

“When I walked by him, he said ‘Nobody move!’ and he shot in the air and I ran,” the employee said.