Holmes also had the day of the shooting marked "with a unique symbol" on a calendar at his home. The movie theater attack occurred during a showing of the Batman film The Dark Knight Rises in July 2012. Twelve people were killed and 70 others were wounded.
Holmes' attorneys have admitted that he was the gunman, but he has entered a not guilty plea by reason of insanity to murder charges. Prosecutors are seeking the death penalty.
FBI agent Leslie Kopper testified that an evidence team found the mask and the uniquely-marked calendar. Kopper didn't elaborate about the discoveries.
Aurora police Detective Thomas Wilson testified he found the violent drawing in a spiral notebook inside Holmes’ backpack. He said the drawing was "some kind of maze game involving a serial killer."
The defense is arguing that the evidence from Holmes' apartment should not be admissible during his trial because it was collected before police had a search warrant.
2014: The Year in Music [PHOTOS]