A harrowing 911 call has revealed the Aurora gunman fired more than one a shot a second at a screening of The Dark Knight Rises.
The call was played on Tuesday in court during a pre-trial hearing at which the prosecution is outlining its case against the accused, James Holmes.
It was claimed at least 30 shots could be heard during the 27-second call, which came 18 minutes into the showing.
Police also played a 911 call from a teenage cousin of six-year-old Veronica Moser-Sullivan, the youngest person to be killed in the Colorado cinema.
A dispatcher tried to talk her through CPR resuscitation but she could not hear because of the noise in the auditorium.
Holmes stared straight ahead as the calls were played, showing no emotion.
FBI bomb technician Garret Gumbinner described how Holmes allegedly set up an elaborate booby trap system to pull police away from the cinema.
The device included improvised napalm and thermite, which burns so hot it cannot be extinguished with water.
Mr Gumbinner said three different ignition systems were found in Holmes’ apartment.
A thermos full of glycerin was placed over a skillet full of another chemical. Flames and sparks would have been created if they were mixed and a trip wire linked the thermos to the door.
Police said Holmes hoped a boom box on a timer would lure someone to the apartment.
The hearing, in Centennial, Colorado, will determine whether Holmes should stand trial.
Twelve people were killed and dozens more wounded after shots were fired at the packed Batman screening in the Denver suburb.
Defence lawyers will call witnesses on Wednesday.
They are expected to highlight Holmes’ mental instability as a possible reason he should not go on trial.
Curious behaviour by Holmes during police questioning has already been detailed.
At one point he tried to stick a metal staple into a power socket. At another he played hand puppets with gloves that had been put on him to preserve evidence.
On Monday, one of the first police officers at the scene told the court he initially thought Holmes was a policeman because he was wearing body armour and a gas mask.
Holmes could face the death penalty if convicted, but lawyers are expected to plead insanity if the case goes to a full trial.