District Attorney Alan Nash presented powerful opening arguments Wednesday in the trial of Eddie Routh, the man accused of killing Chris Kyle, author of American Sniper, and his friend Chad Littlefield.

Nash told the jury of 10 women and two men that when Routh shot and killed Kyle and Littlefield on Feb. 2, 2013 at a gun range at Rough Creek Lodge, Routh was a "troubled young man," but knew the difference between right and wrong.

"Mental illness does not deprive people from being good citizens," Nash told the jurors.

He called Kyle and Littlefield "best friends" who enjoyed spending time together.

"One of the passions they had was befriending and spending time with veterans," Nash said. "And they planned to do that with a man they had never met - the defendant."

He said on the morning of the murders, Routh smoked marijuana and drank whiskey before Kyle and Littlefield picked him up at his house before heading to Rough Creek.

On the nearly two hour trip, Nash said Routh was sitting in the backseat of Kyle's truck.

"We will never know what the conversation was that day," Nash said.

But a text message Kyle sent to Littlefield on the ride gave a glimpse at what the two men thought of Routh.

"This dude is straight up nuts," the text read.

Littlefield responded, "He's right behind me, watch my six."

Hours later, both men were found dead by an employee of Rough Creek Lodge.

Kyle was shot five times in the back and side and once in the head. Littlefield suffered seven gunshot wounds - four in the back, one in the hand, one in the face and one in the head.

Nash said after fleeing in Kyle's pickup with a loaded gun, Routh drove to his uncle's house to show him his "new pickup" and "new guns."

He then stopped at Taco Bell for a burrito before heading to his sister's house, where he told her he had just murdered two men.

The sister called 9-1-1, and a short time later, Lancaster police found Routh at his home, sitting in Kyle's truck.

Nash said Routh refused to get out of the truck and led police on a high speed chase that ended on I-35.

Routh's defense team did not dispute the fact that he committed the murders, but said he was in a psychotic state when they occurred.

"He thought he had to take their lives because in his psychosis, he thought they were going to take his," said Tim Moore, one of Routh's defense attorneys.

Moore outlined a history of mental illness saying Routh had been in and out of a mental hospital and veterans hospital for years.

He said on Jan. 25, 2013 - about a week before the murders took place - Routh was released from the hospital against his family's wishes.