Police are still gathering evidence at the site of Wednesday's tense hostage standoff at the Discovery Channel headquarters.

By morning, police had discovered four bombs gunman James Lee carried in backpacks, including two made with propane.

They're also gathering evidence from when Lee stormed into the building and took three workers as hostages.

At one point Lee ended up on the phone with NBC producer Rob Rivas, who had called Discovery as word spread about the ordeal.

Rivas alerted police and was instructed by officers to keep Lee talking.

"They wanted us to continue chatting with him, and it was my thought that obviously if he was talking to me he wasn't doing anything else in the building," Rivas later said.

After 10 minutes, Lee ended the phone conversation, but the standoff continued for nearly another four hours until he was seen pointing his gun at one of his hostages.

At that point police moved in and opened fire, killing Lee.

Lee's body was removed Thursday morning.

Investigators are now looking at his long-running beef with the Discovery Channel over a lack of programming about global warming and animal extinction.

Investigators say lee's last known address is a homeless shelter in the D.C. area.