"American Sniper"—the Clint Eastwood blockbuster about real-life Navy SEAL sniper Chris Kyle—has broken record after record at the box office. But the story of the man who inspired the film is far from over.

Kyle was murdered in 2013 at a gun range by a troubled Marine, Eddie Ray Routh. Routh is now on trial for murder, with his defense team claiming he suffered from PTSD.

That claim has drawn criticism from some veterans groups like The Warfighter Foundation, who say Routh did not serve in combat and therefore cannot use PTSD as a defense. Homeland security expert Juliette Kayyem disagrees.

"I don't think we should view the PTSD defense as contingent on combat in the same way we should not have argued—and now the Pentagon has changed the rules—that women couldn't get the benefits of having died in war, benefits to their family, benefits of honor and other things, simply because they technically weren't in combat," Kayyem said.

"I don't know if it's right that he had PTSD, but I'm not fixated on the combat issue," she said.

Kayyem stressed that PTSD, if indeed found to be a factor, might not have been the only one. Family members of Routh have suggested that he suffered from other mental disorders. She hypothesized that the Army's drive to increase its ranks may have led to recruits like Routh slipping through the cracks.

"I don't know his history, but did the standards for becoming a Marine or entering the Army change so we could get more bodies in the pipeline? The Army has always contended their standards have not changed," she said.

"I find that hard to believe," she continued.

To hear more from homeland security expert Juliette Kayyem, tune in to Boston Public Radio above.