Feature: Colorado's "brilliant" mass murderer rigged apartment with explosives prior to theater shooting

In an audio tape released in court Tuesday, Denver theater shooter James Holmes told detectives how he had placed explosives in his apartment, trying to outsmart firefighters who would use water to extinguish the inferno he had planned.

Holmes told police he had hoped a huge explosion at his nearby apartment would divert them from responding to the massacre he had planned at the midnight showing of the Batman premiere "The Dark Night Rises."

"You should know that," he told a police detective about Magnesium's burning power, in an interview 15 hours after he walked into a packed theater in the summer of 2012 with three guns and shot 70 people, killing 12.

Magnesium is a highly flammable metal, burns at 4,000 degrees Fahrenheit and is impossible to extinguish, even with water.

Holmes, who had rigged his apartment with explosives to "kill as many as possible," also created Napalm, which can generate a very hot, sticky paste that burns through anything it touches.

"If an officer had set it off... the whole place would have exploded -- killing or maiming anybody in the apartment," FBI Special Agent Garrett Gumbinner said.

Gumbinner was on the stand longer than any witness in the trial thus far, testifying Tuesday about his investigation of the apartment Holmes had rigged, just before he drove to the theater for his shooting spree.

For the first time, Gumbinner showed pictures from a robot camera that nudged open the door to Holmes' apartment later that morning and took pictures of his living room filled with incendiary devices.

The pictures accompanied an all-telling interrogation, during which Holmes, sounding monotone and without emotion, told in great detail how he had rigged his apartment in east Denver with a "fishing wire" to trigger a room filled with explosives.

Instead, a robot was used to nudge open the door to Holmes' apartment, apparently narrowly missing the trip-wire by several inches.

The robot took pictures of the room, filled with numerous chemical explosives that were shown in court Tuesday for the first time.

The robot then "defused" a tilted thermos of Glycerin ready to spill into a "frying pan filled with Potassium Permanganate" connected to a trip wire, the FBI said.

The chemical interaction would have caused an immediate explosion, according to experts.

Holmes also put another "igniter" in a remote-controlled car he had placed outside his building next to a dumpster, hoping someone would pick it up and touch the remote control.

On July 20, 2012, in the densely populated suburb of Aurora that abuts Denver, America's mile-high city, Holmes broke into a threater and set off a tear-gas canister, then ripped hundreds of bullets into the audience, including a 6-year-old girl.

Holmes is trying to avoid the death penalty by claiming the insanity defense.

If found insane, which is likely, Holmes will spend the rest of his life in jail and avoid execution, under U.S. law.

While the defense struggled to show examples of Holmes' sudden decline into schizophrenia, the prosecution produced a mixed bag of witnesses, including an FBI bomb expert, Holmes' mentor in college, and one of the victims -- a mother who had screamed for her children in the dark, smoke-filled theater.

Robert Holmes, father of the admitted mass murderer, sat behind his son with his wife Arlene during the trial. He put three fingers into his mouth when hearing of his son's newly acquired knowledge of pyrotechnics and explosives.

The Holmes can be considered "intellectual," having spent their lives surrounded by academic elites and living a cushy lifestyle in sunny San Diego, California.

After a period of lethargy, Holmes, a graduate with a 3.9 GPA at the University of California, Riverside, was admitted to the Ph.D. programs at the University of Colorado, after rejections from six other schools.

Sukumar Vijayaraghavan, Holmes' mentor, said the school wanted Holmes to join the program because of his high "testing" acumen, but admitted to the jury that Holmes was a "complete mystery" to him. Endi