Holmes, who was arrested outside of The Century Aurora 16 multiplex within minutes of the killings, has not yet been charged and Chief Judge William Sylvester told prosecutors they had until next Monday to file their case, which is likely to include a dozen murder charges, and possibly terrorism.
Relatives of several of the victims were in the small courtroom while others watched on a close-circuit television from within the Arapahoe County Justice Centre. In the front row sat Tom Teves, whose son Alex was among the 12 dead. Mr Teves stared at Holmes throughout the hearing.
Speaking outside of the court, District Attorney Carol Chambers promised that her prosecutors would methodically pursue the case and treat Holmes "like any other defendant".
Ms Chambers said that prosecutors were still "weeks or months" away from making any decision on whether to press for the death penalty but promised that she would "consult widely" with survivors and victims families before making her decision. A capital punishment conviction would likely to lead to years - if not decades - of appeals and hearings that could add to the distress of victims' families.
The prosecutor said she "no information" on Holmes's confusing demeanour inside of the courtroom.
Holmes was said by police to be refusing to cooperate and was due to return the Arapahoe County Jail, where he has been held in solitary confinement for his own safety.
Prosecutors said they did not know whether Holmes would return to court to hear the charges filed against him on July 30. His family said they would make a statement through their lawyer later in the day.
Legal experts speculated that Holmes's defence lawyers may try to plead insanity on behalf of their client but in public statements police seemed eager to head off that possibility.
Aurora Police Chief Dan Oates described both the killing and the subsequent booby-trapping of Holmes's apartment as evidence of "calculation and deliberation".
