SILVER SPRING, Md. (WUSA) -- The video shows everything from the moment James Jae Lee entered the building to the moment he was shot by police.
Lee took three people hostage at the Discovery Channel September 1.
Montgomery County Police shared the surveillance footage with security experts Tuesday during a workplace violence seminar in Silver Spring.
Assistant Chief Wayne Jerman says police didn't have access to the footage until the standoff was over.
The video shows Lee putting on a vest he made, using oxygen tanks, bullets, and a pipe bomb. Soon, a man walks through the door, ducks to the ground, and crawls across the floor.
Jerman says a hostage negotiator talked with Lee on the phone for nearly four hours:
Lee: "I have nothing else to live for."
Negotiator: "Now why do you say that Mr. Lee? What do you mean you have nothing else to live for?"
Lee: "This is it. This is the end, alright."
Police say the hostages used hand gestures to devise a plan to escape. The video shows what happened at that moment.
Lee was killed by police. Jerman says in his pocket was a thumb drive with two videos. Both were made by Lee showing him test his pipe bombs.
Jerman says Lee planned to die that day. An entry on his Outlook calendar read "The End." Jerman says he doesn't know why Lee's pipe bombs failed to explode that day.