BRIDGET CANTRELL HAS READ the stories—the details of Army Staff Sergeant Robert Bales’s solo raid through two Afghanistan villages on the night of March 11, 2012. How he walked over a mile from his base and then zigzagged from house to house, shooting and stabbing and killing 17 Afghans, mostly women and children.

But unlike many who’ve learned about the murder spree, Cantrell doesn’t see Robert Bales as a monster. The Bellingham-­based clinical psychologist, who specializes in military cases, sees the soldier as a casualty himself. “He’s had four tours in Iraq, he was wounded, he did some gruesome things…. And those are all the criteria for PTSD.”

Those following the Afghanistan massacre coverage will be hearing a lot about posttraumatic stress disorder in the coming weeks and months. Bales, who was deployed from Joint Base Lewis-McChord near Tacoma, has retained the legal services of Seattle attorney John Henry Browne, known for defending high-profile clients (see: Ted Bundy, Barefoot Bandit).

Browne has already begun to bandy about the PTSD defense in the court of public opinion. He told CNN, “Anybody that has seen what he’s seen and done what he’s done at the request of the military…I think, would have PTSD. I don’t know, I’m not an expert in that arena.”

Cantrell is an expert in that arena. The daughter of a World War II and Korean War veteran—who was also a PTSD sufferer—Cantrell, 58, knows the disorder and how it affects men and women in uniform like few civilians ever will. She has spent the past 20 years counseling soldiers from every conflict since WWII, and is a member of the mental health team in the Washington State Department of Veterans Affairs PTSD Program. In 2004, the U.S. Army asked her to treat paratroopers of the 173rd Airborne Brigade in Vicenza, Italy. And her books (particularly Down Range: To Iraq and Back and Once a Warrior: Wired for Life) dissect the causes and effects of military-based PTSD, and practically foretold the March massacre in Afghanistan.

“To be chased by a police car…they’re running on adrenaline. In combat…they’re running on adrenaline.”

“The trigger can be a smell, sound, or any combination of many other sensory perceptions that may be associated with a past injury or threat,” Cantrell explains on her website, heartstowardhome.com. “When these sudden triggers occur a veteran may suffer tremendous emotional upset. The pain, fear, helplessness, and confusion of horrific wartime experiences might surface immediately.”

Cantrell uses this reasoning when she works with the attorneys of defendants who’ve come home from a deployment only to be embroiled in criminal cases. Let’s say a soldier is charged with evading police after a routine traffic stop, says Cantrell. “I reframe the case and put it in a container that people can understand: Well, this is where they were when their trigger got tripped and they went into this mode. To be chased by a police car…they’re running on adrenaline. And when they’re in a combat zone…they’re running on adrenaline.”

Cantrell has yet to be contacted by John Henry Browne, though she did send the attorney her books shortly after the Bales story broke. She hopes she gets a chance to speak with the accused staff sergeant. “I would love to spend time with him and get into his situation.”

How do you prove PTSD? You don’t. Not in any quantifiable way. “This is a science but it’s not a hard science, where you put this polymer with this polymer and you get this reaction.” Instead the accused submit to a battery of tests, questionnaires really, that ask about things like their social interactions; the quality of their relationships compared to prior to the traumatic event; whether they have nightmares; and the quality of their sleep.

Self-professed nightmares and sleeplessness won’t make Bales a free man. But to jurors weighing the possibility of the death penalty, a PTSD diagnosis could make him seem like less of a monster.