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STEPHENVILLE (AP) – After several days of evidence focused on the mental health of the former Marine accused in the fatal shootings of “American Sniper” author Chris Kyle and his friend, the trial of Eddie Ray Routh resumed Monday in Texas.

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Criminal law experts say the case hinges on whether the defense can prove Routh, 27, was insane at the time and did not know the killings constituted a crime.

Complete Coverage Of The Trial

Here is a look at key points of the case:

WHO WAS KYLE?

Kyle served four tours in Iraq and made more than 300 kills as a sniper for SEAL Team 3, according to his own count. He also earned two Silver Stars for valor. After leaving the military, he volunteered with veterans facing mental health problems, often taking them shooting. He took Routh to the shooting range at the request of the troubled veteran’s mother.

The case has drawn intense interest, partly because of Kyle’s memoir. The Oscar-nominated film based on the book has grossed nearly $300 million.

PERSPECTIVES ON ROUTH

Family members have said Routh suffered from post-traumatic stress disorder after serving in Iraq. Defense attorneys say Routh, who was taking anti-psychotic medication, was insane when Kyle and his friend, Chad Littlefield, took the former Marine to a shooting range to provide support and camaraderie. Routh, his lawyers say, believed the men planned to kill him.

But prosecutors have said that Routh was a troubled drug user who knew right from wrong, even with a history of mental illness.

Some of Routh’s psychiatrists at Green Oaks Hospital, the hospital where he was admitted in September 2012 and in January 2013, are expected to take the witness stand.

THE CRIME

On February 2, 2013, Kyle, Littlefield and Routh drove to Rough Creek Lodge and Resort, which besides luxury accommodations has a 1,000-yard shooting range. About 5 p.m., a resort employee discovered the bodies. Kyle and Littlefield lay on the ground amid scattered weapons; each had been shot several times. About 45 minutes later, authorities say Routh pulled up to his sister’s Midlothian home in Kyle’s truck and admitted that he had killed Kyle and Littlefield, then drove off.

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On Thursday, prosecutors presented a video in which officers spoke with Routh as he sat in Kyle’s pickup. He refused to leave the vehicle and eventually sped away, with police in pursuit. The video shows that a police vehicle rammed the pickup, which became disabled along the side of the road.

TRIAL HIGHLIGHTS

Kyle’s widow, Taya Kyle, testified on the first day of the highly anticipated trial, speaking about her husband’s passion for helping veterans and gun safety. Sometimes choking up and occasionally wiping away tears, Kyle testified that her husband and Littlefield were close, and enjoyed spending time with veterans as a way to ease back into civilian life.

Prosecutors filed documents Tuesday saying Routh smoked marijuana, drank excessively and had a history of killing small animals. On the day of the killings, Routh had been drinking and smoking marijuana and threatened his girlfriend with a knife, one of the documents says.

A Texas Ranger testified Friday that authorities found marijuana, a near-empty bottle of whiskey and medication for schizophrenia while searching Routh’s small wood-framed home after the shooting.

The testimony could show that Routh deliberately put himself into a violent state, said Park Dietz, a forensic psychiatrist who examined Andrea Yates, who was found not guilty in 2006 by reason of insanity over the drowning deaths of her five children.

“Voluntarily induced intoxication is not an excuse for the mentally ill,” he said.

In a recorded interview with the Texas Rangers played in court, Routh said he understood what he’d done and wanted to apologize to the men’s families.

“You know what you did today is wrong, right?” the ranger asked.

“Yes, sir,” Routh replied.

WHAT’S AT STAKE

Jurors have three options — to find Routh guilty of capital murder, to find him not guilty or to find him not guilty by reason of insanity. If convicted, Routh faces life in prison without parole. Prosecutors aren’t seeking the death penalty. Even if he’s acquitted, Routh could remain in custody. The Texas criminal code stipulates that in cases involving violent crimes where defendants are found not guilty by reason of insanity, the court can initiate civil proceedings to have them committed.

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