As "American Sniper" murder trial begins, lawyers prepare for fight

STEPHENVILLE, Texas -- Eddie Ray Routh, a 27-year-old former Marine, has been diagnosed with PTSD, a major depressive disorder, schizophrenia and paranoia.

At a Texas gun range two years ago, he shot and killed Chris Kyle of "American Sniper" fame, and his friend Chad Littlefield. Kyle was shot six times. Littlefield seven.

Prosecutor Alan Nash insisted that Routh should be held accountable.

"Mental illnesses, even the ones that this defendant may or may not have, don't deprive people from the ability to be good citizens, to know right from wrong," Nash said in opening statements.

The blockbuster movie "American Sniper" tells Kyle's story. The Navy SEAL had 160 confirmed kills in Iraq, the most in U.S. military history.

After the war, Kyle counseled troubled vets like Routh. He and Littlefield met Routh for the first time when they drove him to the gun range.

And right away, defense lawyer Tim Moore says, they sensed Routh's issues.

"Chris Kyle was sitting in the driver's seat on his cell phone and he texts Chad Littlefield, who is sitting right next to him," Moore said in his opening. "He texts him 'this dude is straight up nuts.'"

"When he took their lives he was in the grip of a psychosis."

Taya Kyle, the first witness, cried repeatedly recalling her husband. She testified Kyle took Routh to the range because "he thought he was doing a good thing."

If convicted of the double murder, Routh faces life in prison with no possibility of parole.