Prosecutors plan to seek the death penalty. Holmes has pleaded not guilty by reason of insanity.
Judge Carlos Samour issued a court order last week concerning potential jurors in the case.
"The Court will instruct prospective Jurors that individual voir dire will last approximately two to three months and that the trial itself may last four to five months," Judge Samour wrote. "As such, they should plan to be available to serve on this case for six to eight months."
Searched for 'Rational Insanity'
Judge Samour said the trial may not actually take that long but it was "better to err on the side of overestimating the duration of the trial."
Meanwhile, Holmes' defense attorneys are trying to block testimony from Aurora detectives about what they found on computers seized from his apartment.
Detective Michael Leiker said in a hearing that Holmes had searched for the term "rational insanity," on two of his devices prior to the shootings at the Century Aurora 16 theater.
Evidence Shows Premeditation
Leiker also found photos on Holmes' cell phone of him showing off his arsenal of weapons just a few hours before the mass shooting.
Prosecutors argue that the photos and his computer searches show that Holmes knew that what he was doing was wrong and that he had planned the shooting months in advance.
The trial is not expected to begin until next year.
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Photo: Mug Shot