STEPHENVILLE, Texas (CNN) -- It took a Texas jury less than three hours to find Eddie Ray Routh guilty of capital murder in the deaths of two men, including Chris Kyle, the author of the bestselling book "American Sniper."
Judge Jason Cashon immediately sentenced him to life in prison without the possibility of parole.
Jurors deliberating the case had three choices: guilty, not guilty or not guilty by reason of insanity.
No one disputed that Eddie Ray Routh shot and killed the men. But defense attorneys said Routh was insane.
Prosecutors dismissed that claim outright.
"Ladies and gentleman, that is not insanity. That is just cold, calculated capital murder. He is guilty of capital murder. He is not in any way insane," said attorney Jane Starnes during closing arguments.
She claimed Routh knew the difference between right and wrong.
Starnes urged jurors to "follow the law," allowing the law to guide them "to the true and correct verdict."
For its part, the defense pointed to Routh's long history of mental illness.
"He killed those men because he had a delusion. He believed in his mind that they were going to kill him," said attorney J. Warren St. John.
Routh's trial comes in the wake of the release of the film about Kyle, a former Navy SEAL who claimed to be the deadliest sniper in U.S. history, with 160 confirmed kills in Iraq.
"American Sniper," directed by Clint Eastwood and starring Bradley Cooper, is already the highest-grossing war movie.
Kyle's autobiography by the same name spent weeks on bestseller lists. He had already risen to fame through his book when he died and was involved in charitable work to help former troops suffering from post-traumatic stress disorder.
Kyle and his friend, Chad Littlefield, took Routh to the firing range as a kind of therapy.
The range is a small, remote part of the sprawling 11,000-acre Rough Creek Lodge, and the men were isolated.
A hunting guide found Kyle, 38, and Littlefield, 35, who also was a veteran, motionless and called 911. The men were dead when officers arrived.