STEPHENVILLE, Texas (AP) -- The former Marine convicted of killing "American Sniper" author Chris Kyle and another man was hospitalized multiple times for psychiatric treatment and was prescribed medication to treat schizophrenia.
He spoke of pig-human hybrids and the apocalypse and was described by Kyle himself as "straight-up nuts."
But jurors found the insanity defense for Eddie Ray Routh failed to meet the legal threshold: a mental illness so severe he didn't know right from wrong. His case illustrates the difficulty of succeeding with such a defense at a time when a Colorado court is preparing to hear similar arguments in the trial over a movie theater shooting in which 12 people were killed.
"The insanity defense is very rare, and it's even rarer that a defendant wins it," said George Dix, a law professor at the University of Texas at Austin.
He said when a brutal crime is committed it's difficult to convince a jury the person accused doesn't "deserve the condemnation that comes from a finding of guilty." He added, "And here, we've got him causing the death of an American hero."
Kyle, a former Navy SEAL sniper, volunteered with veterans facing mental health problems after he left the military. A blockbuster film based on his memoir about his four tours in Iraq contributed to intense interest in the case.
Legal experts say a defense attorney's task to convince a jury that a client is legally insane is even more difficult in cases like that of Routh, who confessed to killing the men, apologized to the family and fled from police.
"If someone is admitting that they committed the murder, it's a pretty tough burden to get a jury to say, `Let's excuse him anyway,'" said Dallas defense attorney Michael Snipes.
Kyle and his friend, Chad Littlefield, were killed after taking Routh to a shooting range on Feb. 2, 2013. Routh's mother had asked Kyle if he could help her son, who she said had suffered from post-traumatic stress disorder after serving in Iraq and Haiti.
But the focus of the trial was not PTSD. Routh's attorneys said he suffered from schizophrenia and was having a psychotic episode at the time of the shootings, and noted that Kyle described Routh as "straight-up nuts" in a text message to Littlefield as they drove to the range.
Prosecutors painted the 27-year-old as a troubled drug user who nonetheless knew right from wrong.
A psychologist testifying for prosecutors said Routh was not legally insane but had a paranoid disorder made worse by his use of alcohol and marijuana. In contrast, a psychiatrist testifying for the defense said Routh had schizophrenia and had described seeing neighbors and friends turning into pig-human hybrids.
Snipes said that ultimately, experts cancel each other out in the minds of jurors, who instead look at the defendant's actions.
Juror Barrett Hutchinson told ABC's "Good Morning America" they were not convinced by the claim that Routh was having a psychotic episode. "He knew the consequences of pulling the trigger," Hutchinson said.
The defense plans an appeal, but Routh's attorney J. Warren St. John said he's not yet ready to discuss specifics.
The jury had three options: find Routh guilty of capital murder, find him not guilty or find him not guilty by reason of insanity. With the conviction, Routh received an automatic sentence of life in prison without parole.
Under a finding of not guilty by reason of insanity, Routh would have faced up to life in a state mental hospital. Experts say he would have had the possibility of release only if the state could no longer establish that he had a severe mental illness and was likely to harm another person if he didn't receive inpatient treatment.
But jurors couldn't be told the potential consequences of that finding, a stipulation St. John called a hurdle. Houston defense attorney George Parnham, who was not involved in the case, said it lets jurors assume such a verdict could mean the defendant "will ride down the elevator" with them.
Parnham represented Andrea Yates, the Houston-area woman convicted of drowning her five young children before being retried and found not guilty by reason of insanity. Yates is now in a minimum security state mental hospital.
He said that for the retrial, the defense focused less on mental health records and experts and more on getting jurors to see into the mind of the woman who Parnham said drowned her children because she thought that if she didn't they would be taken by Satan.
In Colorado, jurors are now being selected to hear the case against James Holmes, who has pleaded not guilty by reason of insanity to killing 12 people and injuring 70 in a 2012 attack at a suburban Denver theater.
As in Texas, Colorado law defines insanity as the inability to tell right from wrong - specifically because of a mental disease or defect. But Colorado is one of only a few states that puts the burden of proving sanity on the prosecution. Once a judge allows someone to plead not guilty by reason of insanity, prosecutors must convince the jury the defendant was sane.
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