"As far as we're concerned, they are entering a plea of not guilty, and what they have done to this point is not sufficient to enter a plea of not guilty by reason of insanity," Arapahoe County Ada Karen Pearson said, according to E! Online.
On April 1, prosecutors will announce whether they plan to seek the death penalty. Holmes is likely to be given truth serum or a mandatory lie-detector test. He is charged with 24 counts of first-degree murder, 116 counts of attempted murder, possession of explosive devices and inciting violence.