As the case against Colorado movie theater shooter James Holmes prepares to go to trial, new evidence has surfaced.

The Wednesday hearing against the suspect revealed that among booby traps at his apartment, authorities also found a Batman mask, a calendar with the day of the attack marked with a "unique symbol" and a violent drawing, according to Fox News.

The significance of the items was not revealed at the hearing, which would determine if evidence found at Holmes' apartment after the shooting could be introduced when the case goes before a jury.

Holmes pleaded not guilty by reason of insanity. His attorneys acknowledge his responsibility for the July 2012 attack that killed 12 and injured 70 others at an Aurora movie theater during a screening of The Dark Knight Rises.

The perpetrator was charged with murder for the massacre.

Other emerging evidence include a notebook of violent drawings Holmes sent to a psychiatrist before the attacks as well as statements he made after his arrest. Computer and bank records of the weapons and explosives he purchased were also found.

Prosecutors are reportedly hoping to use the aforementioned evidence to prove Holmes was sane at the time of the attack. This would allow them to seek the death penalty if he is convicted.

During the pretrial, the defense argued that any evidence from Holmes' apartment should be thrown out because police began searching the apartment without a warrant. Prosecutors, however, said the search was lawful because Holmes had told police he had explosives rigged to detonate in his apartment.