Twenty-four-year-old James Holmes appeared Monday and was also formally charged with 116 counts of attempted murder.
Twelve people were killed and 58 people were wounded or injured. The breakdown of the charges was not immediately clear.
He's also charged with a one count of possession of explosives. Authorities say he booby trapped his apartment.
Holmes was arrested early July 20 outside a Century 16 theater in Aurora during a midnight showing of the new Batman movie.
Legal analysts expect his court the case to be dominated by arguments over his sanity.
Holmes was a student at the University of Colorado Denver before withdrawing last month.
