Dr. Charles H. Nichols and Dr. John P. Gray were the two foremost forensic psychiatrists in the latter half of the nineteenth century in the U.S. However, their rationales differed dramatically. They were involved in four notable murder trials where insanity issues arose: one was a trial for the murderer of a Union officer during the Civil War; in another, a conspirator was tried for the assassination of President Abraham Lincoln; in the third, a temporary insanity plea was supported by a medical expert for the first time in a U.S. courtroom; and the fourth was the trial of the assassin of President James A. Garfield. Pointedly, their differing viewpoints still remain controversial today.