STEPHENVILLE, Texas - Lawyers for an Iraqi war veteran will argue at the start of his trial on Wednesday that he was insane when he fatally shot former Navy SEAL Chris Kyle, whose best-selling autobiography was turned into the hit movie "American Sniper."
Eddie Ray Routh, 27, is charged with murdering Kyle and his friend Chad Littlefield in 2013 at a shooting range about 70 miles (110 km) southwest of Fort Worth. A jury of 10 women and two men will hear the case.
After opening arguments, Kyle's widow Taya is expected to be one of the first witnesses to take the stand.
Legal experts have said it is a tough task to obtain a verdict of innocence by reason of insanity in Texas.
If prosecutors win a conviction, they said they will seek a life sentence, while the defence will argue that he was innocent due to severe post traumatic stress disorder caused by Routh's overseas tours of duty with the US Marines.
Routh's relatives have said he was hospitalised for treatment of mental illness in the months leading up to the Feb. 2, 2013 shooting.
He was taken to the range by Kyle, who had been helping fellow veterans heal the mental scars coming from combat.
The case will be heard at a court in rural Erath County.
Routh's lawyers tried unsuccessfully to have the trial delayed, saying that having the movie in theatres nationwide and basking in the award season's glare makes it difficult for Routh to get a fair hearing.
Kyle, credited with the most kills of any US sniper, has been lionized in his home state of Texas, where he is buried at the Texas State Cemetery alongside some of the state's acclaimed figures.
He is seen by many as a symbol of dedication to country and fellow servicemen.
"American Sniper," directed by Clint Eastwood and starring Bradley Cooper, has grossed more than $282 million (S$383 million) since opening in mid-January and has been nominated for six Academy Awards, including best picture.
Routh is accused of stealing Kyle's truck after the killings and driving it to the home of Routh's sister, who said he confessed to the crimes.
Routh was arrested that day and has been jailed in Erath County on $3 million bond.