A US judge entered a plea of not guilty on behalf of alleged Aurora theater gunman James Holmes on Tuesday, after his lawyers said they were not ready to enter a plea. The judge left it open for lawyers for the 25-year-old to enter a plea of not guilty by reason of insanity at a later date, at Holmes's arraignment for the killing of 12 people in the Colorado town of Aurora last July, AFP reported. Judge William Sylvester set a trial date for August 5.