James Holmes' lawyers made the disclosure at a court hearing Thursday in Centennial, where news media organizations were asking a judge to unseal documents in the case.
Holmes had the same dazed demeanor that he has had in previous court appearances.
The shooting during a midnight showing of the latest Batman movie left 12 people dead and 58 others injured.
Holmes, a 24-year-old former Ph.D. student at the University of Colorado, is charged with multiple counts of first-degree murder and attempted first-degree murder.
(Copyright 2012 by The Associated Press. All Rights Reserved.)