Prosecutors told the judge that they were dropping their bid to obtain a notebook that James Holmes allegedly sent to his psychiatrist weeks before the shooting, in which he reportedly detailed plans for the attack, the Denver Post reported.

Former neuroscience student Holmes, 24, already faced 142 charges including 24 counts of first-degree murder in the case. Details of the new charges were not released because of a gag order on the case.

Holmes was in court for the pre-trial hearing, looking different from his previous appearances, when he still sported the bright red hair that he wore during the attack in an apparent attempt to look like the Joker, Batman's comic-book nemesis. According to the Denver Post Holmes now has short-cropped brown hair and smiled during Thursday's hearing.

Twelve people died and 58 were injured in the July 20 shooting in an Aurora, Colorado, cinema packed with moviegoers at a midnight premiere of the Batman movie The Dark Knight Rises.

Police arrested Holmes outside the theatre and spent days defusing booby traps he had laid in his apartment.

Holmes' attorneys have claimed that their client is mentally ill and have asked the court for more time to assess his situation.

Prosecutors had asked to see the notebook, which could show Holmes' state of mind prior to the attack. Defence lawyers stridently objected, arguing that the document is a privileged communication between Holmes and his psychiatrist under the doctor-patient privilege.

In addressing the judge, a prosecutor said that continuing to press for the notebook would delay proceedings, and that prosecutors would be given access to it if Holmes pleads not guilty by reason of insanity.