Colorado prosecutors are expected to file formal charges against James Eagan Holmes, the former neuroscience student accused of killing 12 people and wounding 58 others at an Aurora movie theater.
Attorneys will also argue at Monday morning's hearing over a defense motion to find out who leaked information to the news media.
The information included details about a package the 24-year-old former neuroscience graduate student allegedly sent to his psychiatrist at the University of Colorado Denver.
Legal analysts expect the case will be dominated by arguments over the defendant's sanity.
Holmes allegedly began stockpiling gear for his assault four months ago, well before the shooting spree just after midnight during a showing of the Batman film "The Dark Knight Rises." He was arrested by police outside the theater.
© Copyright 2016 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.