This Marine is on trial for allegedly killing real-life 'American Sniper' Chris Kyle

Navy SEAL Chris Kyle is considered the deadliest sniper in US military history. With 160 confirmed kills, he wrote his autobiography, "American Sniper," which led to a hit movie of the same title.

The real-life story has a tragic ending. In 2013, Eddie Ray Routh, a 27-year-old Marine veteran, allegedly shot and killed Kyle. Jury selection began Thursday for his trial, scheduled to start next week.

Finally back on American soil after four tours in Iraq, Kyle started taking veterans to shooting ranges as a form of therapy. When a woman who lived near Kyle heard about his efforts, she asked him to help her son, Routh, then just 25 and reportedly suffering from severe post-traumatic stress disorder (PTSD).

Kyle and his friend Chad Littlefield took Routh to target practice at the 11,000-acre Rough Creek Lodge Shooting Range on Feb. 2 2013 near Chalk Mountain, Texas. That day, Routh allegedly shot and killed both men. No witnesses saw the situation unfold.

Routh has pleaded not guilty by way of insanity.

"Someone taking the lives of two people that were there to help them - that's not PTSD, in my opinion," Kyle's widow Taya told ABC News.

Routh, an expert marksman who served in Iraq and Haiti, admitted to killing Kyle and Littlefield at the range and then driving away in Kyle's truck, according to a police affidavit.

Later that night, Routh allegedly drove to his sister Laura Belvin's house. She told police Routh seemed "out of his mind saying people were sucking his soul and that he could smell the pigs." His brother-in-law also told police Routh said he killed two men at the range.

In another 911 call in September 2013, Routh's mother told the operator Routh had threatened to kill himself and others. Records obtained by the Dallas Morning Show also show that Routh spent time a psychiatric hospital at least twice.

With the popularity of the film - which grossed nearly $250 million and was nominated for six Oscars - finding an impartial jury is a tough task. On the questionnaire, an affirmative answer alone to "Did you see the movie 'American Sniper?'" will disqualify potential jurors.

The location of the trial, the close-knit, military-friendly town of Stephenville, Texas, could also affect the jury's opinion of the case. Consider that Texas Gov. Greg Abbott just declared Feb. 2 "Chris Kyle Day" in honor of the late Navy SEAL sniper. Routh's lawyer already tried and failed to postpone and move the trial.

Prosecutors said they wouldn't seek the death penalty against Routh.