James Holmes, accused of opening fire in a Colorado movie theater in July and killing 12 people, will plead not guilty by reason of insanity, his lawyers said in a court filing Tuesday.
Federal agents have said the 25-year-old former University of Colorado doctoral student had planned the attack at the premiere of the Batman movie "The Dark Knight Rises" for months.
Holmes is scheduled to begin trial next February in a case that is expected to last about four months.
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