The parents of Colorado theater shooting suspect James Holmes are pleading for him to be spared the death penalty.

In a letter to The Denver Post published Friday, Robert and Arlene Holmes say their son is not a monster but "a human being gripped by a severe mental illness." They say that they have spent every moment of the two years since the shooting thinking about the victims and their families and friends.

Holmes has pleaded not guilty by reason of insanity to charges of killing 12 people and injuring 70 in the 2012 attack. Jury selection is scheduled to start Jan. 20.

His parents say a plea deal that would put him in prison for the rest of his life would keep everyone safe and avoid a traumatic trial.