STEPHENVILLE, Texas (AP) — Shortly before he was shot to death by a troubled former Marine at a Texas gun range, legendary Navy SEAL sniper Chris Kyle texted a buddy, “This dude is straight-up nuts,” a defense attorney told jurors Wednesday.

A lawyer for Eddie Ray Routh said in opening statements of the man’s murder trial that Routh’s insanity was so evident that Kyle and his friend Chad Littlefield exchanged texts expressing alarm as the three rode together in February 2013 to a Texas shooting range.

“He’s (sitting) right behind me, watch my six,” Littlefield texted back, using a military reference for watching one’s back.

But a prosecutor said Routh still knew right from wrong, even with a history of mental illness.

The first day of the highly anticipated trial also included sometimes tearful testimony from Kyle’s widow, who spoke about her husband’s passion for helping veterans, gun safety and opposition to mixing alcohol with gun use.

The case has drawn intense interest, largely because of Kyle’s memoir about being a sniper who served four tours in Iraq. The Oscar-nominated film based on the book has grossed nearly $300 million.

Erath County District Attorney Alan Nash described the 27-year-old Routh as “a troubled young man” who on the morning of the killings numbed himself with marijuana and whiskey. He said a history of mental illness should not absolve Routh of being accountable for the deaths.

“The evidence will show that mental illnesses, even the ones that this defendant may or may not have, don’t deprive people from being good citizens, to know right from wrong,” Nash said.

Tim Moore, an attorney for Routh, said Kyle and Littlefield’s text exchange shows how Routh was spiraling out of control. He told jurors that Routh was suffering from severe mental strain that day and thought he needed to kill the two or they would turn on him.

“He thought he had to take their lives or he was in danger,” Moore said.

Kyle’s widow, Taya Kyle, choked up and occasionally wiped away tears during her testimony. She had military dog tags around her neck for part of her testimony and clutched them in her hands at other times.

She said her husband had been approached by Routh’s mother to help her son. Chris Kyle took Routh to the shooting range at Rough Creek Lodge and Resort because it was located in beautiful country side and allowed for time to talk on the hour-and-a-half drive.

She said that as her husband left to go to the range, “we just said we loved each other and gave each other a hug and kiss.”

She later called him around the time he arrived at Rough Creek and noticed her husband was unusually terse in their conversation. “It was short, like, `I wish I could say more,'” she said.

The widow testified that Littlefield and her husband were close, and enjoyed spending time with veterans as a way to help them ease back into civilian life. She detailed her husband’s own struggles after leaving the battlefield, saying he had post-traumatic stress disorder, was irritable and slowed by physical ailments.

The defense asked if her husband could recognize when someone had been drinking before firing weapons, suggesting that Chris Kyle and Littlefield should have known as they rode with Routh that he was intoxicated.

Taya Kyle said her husband didn’t condone drinking while using weapons, and testified that he was upset when he once attended an event where people who had consumed alcohol were firing weapons.

An employee at Rough Creek testified that he came upon the bodies of Kyle and Littlefield at the shooting range as he took a young guest and his father to meet Kyle. Both men were shot multiple times.

Graphic photos of the crime scene had been shown earlier, with Taya Kyle first stoic, then visibly upset as more close-up shots were shown. A couple of jurors also became tearful.

The intense attention on the case has brought renewed focus to the mental struggles former military members face.

Routh was a small arms technician who served in Iraq and was deployed to earthquake-ravaged Haiti before leaving the Marines in 2010. Authorities say that after the February 2013 shooting, Routh drove to his sister’s house in Kyle’s truck, admitted to the killings and told his sister “people were sucking his soul.”

Routh faces life in prison without parole if convicted.