FBI bomb technician Garrett Gumbinner, who interviewed Holmes on July 20 hours after the massacre, described the system at a preliminary hearing. He said the plan included a gasoline-soaked carpet, loud music and a remote control car.
He said he rigged the apartment to explode to get law enforcement to send resources to his apartment instead of the theater," Gumbinner said.
Gumbinner said three different ignition systems were found in the apartment. There was a thermos full of glycerin leaning over a skillet full of another chemical. Flames and sparks are created when they mix, and a trip wire linked the thermos to the door.
Prosecutors are laying out their case in the attack that killed 12 and wounded dozens, trying to show that it was a premeditated act and that Holmes should stand trial. Defense attorneys say he is mentally ill.
Officer Jason Oviatt testified that when police first arrived at the theater and saw Holmes standing next to his car, he thought he was a policeman because of how he was dressed, but then realized he was just standing there and not rushing toward the theater. He said Holmes seemed "very, very relaxed" and didn't seem to have "normal emotional reactions" to things. "He seemed very detached," he said.
After arresting Holmes, Officer Justin Grizzle asked him if anyone had been helping him or working with him. "He just looked at me and smiled ... like a smirk," Grizzle testified.Also on Tuesday, two new 911 calls were released in court. One was the very first call from moviegoer Kevin Quinonez as the shooting was still under way. At least 30 rapid-fire gunshots could be heard in the background of the 27-second call, along with screaming. The call came in 18 minutes into the showing of "The Dark Knight Rises".
Police also played a 911 call from a teenage cousin of 6-year-old Veronica Moser-Sullivan, the youngest person killed. A dispatcher tried to talk her through CPR but she sounded panicked and said she couldn't hear.
Holmes stared straight ahead as the calls were played and didn't show any emotion. He is charged with more than 160 counts, including murder and attempted murder.
ABC News and The Associated Press contributed to this report.