(Andy Cross/The Denver Post/AP Photo)

ABC News' Clayton Sandell and Carol McKinley report:

Attorneys for James Holmes admitted their client committed the mass shooting last July at an Aurora Colorado movie theater, claiming he was "in the throes of a psychotic episode."

Holmes has already pleaded not guilty by reason of insanity, leaving little question about who committed the shooting.

Court accepts James Holmes insanity plea in Colo. theater massacre.

The revelation contained in a new defense motion, however, is the first time his lawyers have been so explicit about his responsibility for the July 20 shooting that left 12 people dead and another 70 shot or injured.

"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 motion read.

The defense motion objected to an earlier ruling from the judge requiring Holmes to wear a harness and be anchored to the floor of the courtroom during trial for safety.

"Other than the nature of the charges in this case, there is no evidence that Mr. Holmes presents a danger to the safety of the courtroom or a flight risk of any kind," his attorneys wrote.

The defense team claimed that using the restraint is analogous to hitching an animal to the floor. That got a quick response from Judge Carlos Samour, who said the defense motion, "while high on rhetoric, is low in substance."

"Inasmuch as the defendant is charged with 24 counts of first degree murder and 140 counts of attempted first degree murder following a shooting at two adjacent Aurora move theaters, it is not appropriate to allow him to be unrestrained during trial," Samour wrote in an order.

Former Adams County, Colo., prosecutor Bob Grant believes Holmes' lawyers are looking for any issue they can use to launch an eventual appeal. The defense believes having Holmes appear in restraints may also prejudice the jury, Grant said.

"The theory is if the jurors believe Holmes is in jail, he must have done something wrong," Grant told ABC News.

Denver criminal defense attorney Larry Pozner said that lawyers admitting Holmes pulled the trigger should not come as a surprise.

"It's the right move," Pozner said. "But they already made that call when they offered to plead guilty to first-degree murder in exchange for life in prison. This is not new and different."