The lawyers' first-ever admission of their client's actions was made in a motion filed Tuesday and made public Wednesday, The Denver Post reported.
"[The] evidence revealed thus far in the case supports the defense's position that Mr. Holmes suffers from a severe mental illness and was in the throes of a psychotic episode when he committed the acts that resulted in the tragic loss of life and injuries sustained by moviegoers on July 20, 2012," the lawyers said in the motion.
Holmes pleaded not guilty by reason of insanity to 166 counts of murder, attempted murder and other offenses. This week's motion is the first time Holmes' attorneys explicitly said he committed the mass shooting.
The motion was one of two Holmes' attorneys filed this week. Both criticized Judge Carlos Samour's decision that Holmes must be restrained during trial, the Post said.
Holmes' lawyers said their client "never once presented as anything other than compliant and well-behaved" during court appearances and argued Samour's order is "incorrect, troubling and inhumane."
In the second motion, Holmes' lawyers criticized Samour for meeting with the Arapahoe County Sheriff's Department concerning courtroom security without the defense present.
Samour rejected the motions and chided Holmes' attorneys for filing them. Because of the charges against Holmes, Samour said, "it is not appropriate to allow him to be unrestrained at trial."
The Post said Holmes is believed to be undergoing a court-ordered mental health evaluation as part of his insanity plea.
Holmes' trial is scheduled to begin in February. Prosecutors are seeking the death penalty.