Lee was arrested in 2008 for disorderly conduct during a protest outside of Discovery Channel headquarters.
Tuonglan Lee said his mental state diminished over time. "Two people close to him died in 2002, and after their passing he became angry and very emotional. He had a normal relationship with people before 2002, but after that he was completely different."
Lee's brother told ABC News that Lee was likely seeking to be killed by the police.
"It was definitely out of character," Aaron Lee said. "I thought it was insanity. I was sad to know that he was shot and killed, but that's what he probably wanted."
Lee, 43, was killed Wednesday as he brandished a gun and wore an explosive device in the lobby of the Discovery Channel headquarters where he had taken three people hostage.
"Any time that police officers use deadly force, it's to save a life... In this situation the hostages -- who were tremendously courageous throughout this incident -- were in grave danger," Montgomery County Police Chief J. Thomas Manger told "Good Morning America."
Manger said that SWAT officers had been able to sneak "very close" to Lee without alerting him, close enough to hear a disconcerting "pop."
"SWAT officers heard a shout, they heard a pop. They were unclear if that was a gunshot or if it was the suspect detonating a device," Manger said. "The officers immediately confronted the suspect. He had a gun out and he was shot at that point."
After Lee was killed and all the hostages safely evacuated, police found several makeshift explosive devices both strapped to Lee's body and in a box and bag that he had brought into the building. In addition, police recovered a second handgun and a ski mask.
"Attached to propane cylinders, he had pipes that contained shotgun shells. In addition he had a couple of pipe bombs strapped to it. They appeared to have some sort of firework type material inside of them," Manger said.
One of the devices reportedly went off when Lee was shot. The rest were detonated overnight by police who have since swept the building and found no other explosives.
Lee warned that he was wired to explode. Remarkably, the gunman picked up the phone when a reporter for NBC News called the lobby. When asked if he had a gun, Lee responded, "I have a gun and I have a bomb. I have several bombs strapped to my body ready to go off."
It's believed Lee invaded the building as the final act in a longstanding protest against the Discovery Channel for promoting what he called an anti-environmental message.
In a rambling manifesto on Lee's website, believed to have been written by Lee, the writer rails against "disgusting human babies," "parasitic infants," and says people should "disassemble civilization." The manifesto also calls on Discovery to "broadcast to the world their commitment to save the planet."
For at least two years Lee called for protests against the company and was arrested and found guilty of disorderly conduct for a protest outside of Discovery's Maryland headquarters in 2008. Due to these past actions, security at the Discovery Channel offices knew who Lee was and "immediately identified" him during this incident, Manger said.
The drama began when workers in the building got a bulletin from the building's security at around 1 p.m.