By Keith Coffman
CENTENNIAL, Colo. (Reuters) - Colorado movie theater gunman James Holmes' apartment was rigged with improvised explosive devices, jars of napalm and fire-accelerating chemical powder sprinkled on the floor, an FBI expert told jurors at his trial on Tuesday.
Prosecutors say Holmes, a 27-year-old former neuroscience graduate student, planned to divert emergency crews by destroying his home in the Denver suburb of Aurora while he opened fire on a packed midnight premiere of the Batman film "The Dark Knight Rises."
Holmes has pleaded not guilty by reason of insanity to multiple counts of murder and attempted murder for killing 12 people and wounding 70 in the July 2012 rampage.
FBI bomb technician Special Agent Garrett Gumbinner, who interviewed the defendant soon after his arrest, showed the jury photos from Holmes' apartment near the theater, some taken with a remote-controlled bomb robot.
He said the images showed a booby trap made from fishing line connecting the front door to a thermos of glycerin, sitting above a frying pan full of potassium permanganate, an explosive combination.
Prosecutor Rich Orman asked what would have happened if the tripwire had been triggered.
"The ... reaction would have caused sparks and flames which would have hit the carpet which was saturated with gas and oil, which would in turn have made the whole apartment explode, killing or maiming whoever was inside at the time," Gumbinner replied.
He said magnesium powder was sprinkled on the carpet. When doused with water by firefighters, it would have strengthened the flames and given off a noxious gas, making it more dangerous for emergency teams. Jars of napalm and bottles of gasoline had been placed on furniture.
An Aurora detective testified that Holmes told him following his arrest that he had set very loud music to start playing 25 minutes after he left for the theater, hoping his neighbors would call police.
Prosecutors say a neighbor did go upstairs to complain, and she even kicked the unlocked door in anger. But she did not open it and went home to phone police.
TOY CAR CONTROLLER
Prosecutors say the defendant linked an incendiary device in his home to a remote control unit for a toy car, both of which he left next to a nearby dumpster that night.
Gumbinner was asked what would have happened if someone had used the toy car's controller, which he said was connected to a "pyrotechnic firing box" in Holmes' kitchen.
"It's my belief that if somebody would have found that remote and R.C. car, and tried to play with the car utilizing that remote, it would have set the apartment off and it would have exploded," Gumbinner said.
Jurors have been played video and audio of Holmes being interviewed by the FBI agent and Aurora police detectives.
Mostly giving slow, one-word answers, Holmes is heard asking in the video whether any children were hurt in the attack and in the audio recording apparently describing the explosive devices in his apartment.
But that audio was particularly poor, and the defense objected to a transcript made by the FBI that was given to jurors, arguing much of it was inaudible.
Arapahoe County District Court Judge Carlos Samour overruled the objection but cautioned the jury of 19 women and five men that the transcript was only a guide.
Prosecutors say Holmes carried out the massacre because he had lost his career, girlfriend and purpose in life.
Holmes' public defenders say he suffers from schizophrenia and heard voices in his head telling him to kill.
The trial is expected to last four or five months.
(Reporting by Keith Coffman; Editing by Daniel Wallis and Cynthia Osterman)