A former Marine was sentenced Tuesday to life in prison without parole after being convicted of murdering the US Navy Seal whose memoir was adapted as the blockbuster movie "American Sniper."

After deliberating for less than three hours, jurors unanimously rejected claims from Eddie Ray Routh, 27, that he was not guilty on grounds of insanity when he killed famed sniper Chris Kyle and his friend Chad Littlefield at a Texas shooting range in February 2013.

The two-week trial in Erath County, about 100 miles southwest of Dallas, attracted massive media attention across America. And it coincided with the release of Clint Eastwood's controversial movie based on Kyle's experiences in Iraq.