Over the next four months, Walker successfully robbed nine more banks. They were mostly small, community banks where tellers and managers knew their customers and treated them with the same Midwestern friendliness they expected from their neighbors. Liliana banked at one of them. Tim conducted business with another. A few, like Chase and U.S. Bank, were national. All were nestled comfortably within strip malls, next to restaurants and hair salons, straddling busy intersections in the kind of sprawling suburban landscapes that surround most American cities.

The first robbery had been done almost on pure impulse, impromptu self-medication, as were subsequent ones. Once, while waiting to pick up Kara from Cleveland State University, Walker told FBI investigators, he robbed a bank as a way "to kill time." In another instance, he was getting gas and made the decision to rob a nearby bank; within 30 minutes he had. But as time went on, and Walker sank deeper into the orbit of the drug dealers from whom he was getting his heroin, he began to take on accomplices. Five of the robberies Walker committed were done with various other criminals from Cleveland's underworld. They started out peacefully enough, with Walker passing notes and asking politely for cash — in one case he told a teller, "It's not personal" before leaving — but culminated in two armed robberies, during which he carried a pistol. According to court documents, during a robbery on March 2, Walker got testy with one of the tellers, saying, "Faster before I have to come back there and do it myself." The teller eventually handed over nearly $5,000 in cash. Later that month, at a Charter One Bank, Walker walked in and yelled, "Robbery, robbery, this is a robbery," but got nervous and left without any money at all.

In Iraq, Walker had grown accustomed to using weapons on a daily basis. He had kicked in doors, invaded people's homes, shot them, and trashed their houses virtually every day. For someone who tended to see things in stark terms, this moral ambiguity was utterly confounding. "Do I appreciate the wrongfulness of brandishing a gun in front of someone?" he asked me. "I don't know… for someone who hasn't been through what I've seen, I guess. But just because the world is terrible doesn't mean you stop trying to be good."

He gave away most of the nearly $40,000 he'd stolen — to friends, dealers and other addicts. Some of it he burned, holding it over his kitchen sink and lighting it on fire, the way he once saw it done in a movie.

It wasn't until he was caught, and doctors had a chance to examine him, that the full measure of Walker's condition began to emerge. In a 36-page report, Pablo Stewart wrote that Walker not only had PTSD but that it was, in his view, a "particularly severe and devastating" case. Stewart argued that Walker's case was exacerbated by his heroism. "PTSD often occurs in individuals returning home from war, and war heroes are particularly vulnerable to the disorder, because the same bravery and willingness to fight that makes them heroic also frequently results in their exposure to significantly more combat and combat-related trauma than other soldiers."

Stewart, who served as a captain in the Marine Corps during the Vietnam era, also challenged Walker's psychiatrist's bipolar disorder diagnosis. That psychiatrist "failed to rule out or even explore the possibility that Nicholas was suffering from PTSD," he wrote, "Once again, an opportunity to properly identify and treat Nick's severe, chronic PTSD was missed, and Nick's problems continued to deepen and indeed to spiral out of control." ("If I thought it'd make a difference, I'd sue the son of a bitch," Tim Walker told me one night as we sat by the pool in their backyard.)

Another physician, John Matthew Fabian, who also interviewed Walker after his arrest and whose report was submitted as part of Walker's defense, gave Walker a test called the Clinician Administered PTSD Score (CAPS). Walker scored a 101, far higher than the 65 that is the clinical threshold for PTSD. In several other tests, his results indicated extreme and chronic signs of PTSD. Furthermore, Fabian posited that Walker had suffered significant damage to his "neuropsychological functioning" and "neurocircuitry," which qualified him as suffering from a "severe mental disease."

As Walker related these stories to me, I looked around us in the prison's waiting room. Walker had tried to get help when he sensed a problem brewing within himself, but was unable to find it. The VA had twice denied him benefits, only to eventually back down, but by then the PTSD was already well-advanced. And now he was here, at Ashland, home, he told me, to a large number of child sex offenders and various low-risk white-collar criminals of various sorts. After initially being refused treatment for his injured back, he eventually was given a brace. Prison had changed him, he told me, made him more sympathetic to people whose habits in his former life would have been unthinkable. His predicament also made him question himself in new ways. When he heard about mass shootings, like in Aurora, Colorado or Newtown, Connecticut, he suddenly wondered: Am I like those killers? And with these thoughts in mind, his heroism in Iraq began to seem like an illusion and a farce.

His fellow soldiers felt differently. In a letter to the court, Spc. David Weinthaler wrote, "I guarantee Walker went on more missions than any other person in my battalion. Which I think says a lot being that he wasn't even infantry. He's the only medic I ever knew that carried an M16 (as opposed to an M9). When he wasn't on patrol he was constantly helping other soldiers with everything from bullet holes to venereal diseases." Walker's platoon leader, Sgt. Anthony Doll, wrote in a letter to the court that Walker "pushed aside any thoughts of self-preservation and subjected himself to the mortal dangers of combat. His unhesitant self-motivation resulted in the continued lives of many young men. I was witness to this."

Walker didn't share that generous assessment. "All those things just happened to me," he told me. "I didn't karate-chop [Abu Musab al] Zarqawi. I'm no fucking hero, I just showed up. I didn't even have a very good success rate for a medic. When I had a chance to save somebody's life, like this guy in the fields, I fucking blew it. And then when people tell you you're some fucking hero it drives you crazy because you feel like some fucking fraud."

In Iraq, a tension would build up before and during each of those missions Walker went on. Most often, these operations would result in violence, always starting with a sudden burst — a roadside bomb, a shot fired, an ambush — the spark that lit the engagement with the enemy. And once that initial symbolic "bang" occurred, tension melted away and was replaced by a rush of calm acceptance, a sort of peace that flooded into every vein of his body. And in that moment, the fear of death and of pain, the rush of nostalgia, and the longing for one's family and friends seemed to wash away as tranquility took over and pure action kicked in. It was incredibly high-stress, but he was accustomed to it, thrived on it, felt comfortable, competent.

I asked him what the equivalent moment was, during a robbery, of the "bang" that occurred in a war. He didn't hesitate: "Passing the note," he said. "During a robbery, passing the note is the 'bang.' Then the die is cast. After that initial contact, there's peace, and you could die then and it doesn't even matter."

He felt, he said, a kind of kinship with the man in the field. Prior to this, I hadn't really understood why this particular event, of all the horrors Walker had seen, had been so painful. "You know, I can relate to him a little. He ran from the police — us — and we killed him. I ran from the police, and now I'm doing 11 years in a federal prison."

Stewart and the other psychiatrists had noted repeatedly that Walker had suffered severe cognitive impairment as a result of his time in Iraq. And precisely because of the heroic nature of Walker's service, his high levels of exposure to violence, his subsequent PTSD was more pronounced and severe than other cases. Upon his return, the world simply didn't make sense in some fundamental way. In Iraq, when Walker would go to dangerous areas, he told me "the ground felt different, it's like you're standing on the ground but it's like you're on a rock wall or a ladder, or slightly above it." This was language that described dissociative behavior, as Stewart and others had pointed out. Walker's brain was still developing during the time he experienced the worst of the war. And Walker had felt that dissociation over and over again until, one day, the chemical and brain changes it engendered were stripped away and Walker was left naked, alone and without a clue as to how to make sense of the world. "It's not that I thought I was doing something wrong — only that I wasn't doing anything worse than what else I had done and seen," he told me. "It was a moral gray area. No good, no bad, or right or wrong, just degrees of shit."

Walker and his legal and medical team considered pursuing an insanity defense. Stewart, for one, had concluded in his report that Walker was not responsible for his actions because of the severe nature of his PTSD. And while Art Hernandez had come around to the idea that Walker was indeed more damaged than he had at first believed, the prosecutor was adamant that Walker would lose if he pursued his insanity defense in court. The fact that he had used a gun during two robberies complicated things further; laws in Ohio meant that Walker faced a 32-year mandatory minimum if he were convicted. So he decided to enter a plea bargain. On June 1, 2012, a federal judge in Cleveland convened Walker for sentencing.

Walker was given a chance to speak. "I would like to apologize to the to the bank tellers, the bank workers, the drivers, passengers that I endangered and who I intimidated and frightened," he told the court. "I also would like to apologize to my family and loved ones, who have suffered so much throughout this ordeal."

He continued, talking about the robberies themselves: "They were not organized or thought out, they were acts of desperation. In the shape that I was in, I couldn't really imagine how I could continue living like I was, but at the same time, I was afraid of addressing the issues and exposing myself because I was ashamed of the state that I was in and just how far gone I was at the time."

Then the judge addressed Walker: "Even in the state that you were in, what was the catalyst or the motivation to rob a bank?"

In his somewhat rambling answer, Walker repeated, "I don't know" many times, finally saying, "I have been very desensitized to things like this, and I am not trying to be insolent at all, but at the time, it just didn't seem like that extraordinary, you know, such a terrible thing to do, which it is, and I realize that now, but at the time, for some reason, I thought it was not normal but not as insane as it looks in retrospect."

The judge gave Walker an 11-year sentence, almost a year less than the 12–15 range that had been agreed upon between the government and Walker's attorneys, "because the defendant accepted responsibility" for his crimes.

After the sentencing, Hernandez went to see Walker in prison. Hernandez was himself a Marine who had also served in Iraq as an aviation logistics officer, but with no combat exposure whatsoever. Hernandez declined to confirm the meeting, but according to Walker and Walker's lawyer, Angelo Lonardo, who was also present, Hernandez said he wanted to talk to Walker "soldier to soldier."

"He gave me some real good encouraging words," Walker recalled, "He said, 'I deal with a lot of people who aren't very kind people, who don't feel remorse, and I can tell you're a good guy. I know you feel bad, your life's not over. You can go on and heal yourself.'"

The first book Walker read when he arrived in prison was

. These days, he spends a lot of time studying Latin and listening to classical music. In Latin he finds enjoyment in the puzzle-like quality of verb conjugation and tense agreement. The classical music brings him peace and tranquility. He speaks to his parents by phone all the time, and they come for monthly visits.

Many of Walker's fellow soldiers have also gone through rough times. One of them was court martialed. Some committed suicide. As close as he was to them during the war, Walker has no lasting desire to be in regular touch with them anymore. "I wouldn't expect anything of anyone," he told me. "A lot of people had a lot of issues."