"It was just another day in Mosul," the soldier began, his voice shaking. Sgt. 1st Class Marshall Powell took a deep breath. He couldn't look at the other three servicemen in the group therapy session.

He'd rarely spoken about his secret, the story of the little girl who wound up in his hospital during the war in Iraq, where he served as an Army nurse. Her chest had been blown apart, and her brown eyes implored him for help. Whenever he'd thought of her since, "I killed the girl," echoed in his head.

Powell kept his eyes glued to the pages he'd written.

He recalled the chaos after a bombing that August day in 2007, the vehicles roaring up with Iraqi civilians covered in blood. Around midnight, Powell took charge of the area housing those with little chance of survival. There, amid the mangled bodies, he saw her.

She was tiny, maybe 6 years old, lying on the floor. Her angelic face reminded him of his niece back home in Oklahoma.

Back in the therapy room, saying it all out loud, Powell's eyes began to fill just at the memory of her. "I couldn't let her lay there and suffer," he said.

A doctor had filled a syringe with painkillers. Powell pushed dose after dose into her IV.

"She smiled at me," he told the others in the room, "and I smiled back. Then she took her last gasp of air."

___

Before the war, Sgt. Powell's very core was built on God and faith and saving lives, not doing anything that could end one. He lost his purpose when the girl died, and he found himself in a nondescript room on a San Diego naval base trying desperately to save his own crumbling existence.

Surrounding him that day were veterans who had suffered as he suffered: An Army staff sergeant who stood frozen in shock, unable to offer aid to a fellow soldier whose legs were severed in an explosion in Afghanistan. A Marine whose junior comrade was fatally shot after he convinced him to switch posts in Iraq. A Navy man who beat an Iraqi citizen in anger.

Like Powell, they'd spent years torturing themselves over acts that tortured their conscience. "Souls in anguish" is how some experts describe this psychological scar of war now being identified as "moral injury."

Unlike post-traumatic stress disorder, which is based on fear from feeling one's life threatened, moral injury produces guilt and shame from something done or witnessed that goes against one's values or may even be a crime.

While the idea of warriors feeling remorse over battlefield horrors is not new, moral injury has gained more attention following the wars in Iraq and Afghanistan as mental health providers point to it as a reason why veterans aren't improving with PTSD treatments.

The Navy now runs one of the military's first residential treatment programs that addresses the problem — the one that Powell found.

Still, debate persists over whether moral injury is a part of PTSD or its own separate condition. There is no formal medical diagnosis for it.

Psychiatrists who treat moral injury believe it has contributed to the suicide rate among veterans, who account for 1 out of every 5 suicides in the United States. And they see danger in ignoring it because its treatment is distinct.

PTSD sufferers can find relief with medication and counseling that encourages reliving the triggering incident to work through fear. But if the person considers what happened to be morally wrong, reliving it may only reaffirm that belief.

Counselors have found the self-punishment stops when veterans learn the deed does not define who they are. Veterans, the experts said, find comfort in sharing with each other, because only those who've experienced war can truly understand the complexity of morality on the battlefield.

"The pain brings everyone together and creates a bond that no one can break," said Elvin Carey of Murrieta, California, whose fellow Marine died after the two switched posts.

___

Sgt. Powell is a friendly man who finds peace working on his family's farmland outside Crescent, Oklahoma. He said he wanted to share his story because it might prompt others to seek help.

And while Powell always blamed himself for the girl's death, three toxicology experts interviewed by The Associated Press said her injuries, not the drugs, likely caused her death.

By the time he arrived in San Diego in February 2014, Powell, then 56, was on therapist No. 5 and contemplating suicide. He had never heard of moral injury; he just knew that the beliefs that had shaped his life were shattered.

He was raised on the idea that God has a reason for everything. It was the mantra his family drew strength from in the face of poverty and racism in rural Crescent.

"When a man's down, if he stays down, he done lay down," Powell's older brother, Bob, said once when young Marshall flopped down on the porch, upset over being called a racial slur at school. "You need to get on up from there."

He learned to pick himself up from even the darkest depths. After Bob died in a car accident, Powell, then in the Air Force, started using drugs, quit the service and wound up sleeping on the streets of Dayton, Ohio. He returned to Crescent and to Sunday services, apologizing to the pastor for having only a dime to drop in the basket. The reverend gave it back, along with $43 in donations, and told him to keep his faith. "God hears you," said the pastor.

The next day, Powell joined the Army.

But the girl was something he couldn't get back up from. Months after her death, Powell was sent back stateside to Hawaii. Soon, she was appearing in his dreams.

Her death left him questioning God, and himself most of all. Powell started drinking heavily and sought help for PTSD. He was prescribed pills for insomnia, depression and anxiety. But, he says, "I couldn't beat it." After six years, a therapist recommended the program at Naval Medical Center San Diego.

Called Overcoming Adversity and Stress Injury Support, or OASIS, the program started in 2010 with the aim to help service members not finding success with PTSD treatments. Three years later, therapies addressing moral injury were added.

Seven other servicemen were part of Powell's 10-week session. After the second week, the veterans were asked to put in writing what had triggered their moral injuries. After a month, the men were divided into two groups to share their stories.

When Powell was finished, the men in the room were silent at first. Among them was Carey, who, listening to Powell, felt a connection to someone for the first time in years. Steven Velez was there, too, flashing back to his time as an Army staff sergeant in Afghanistan, when he was too traumatized to help his comrade. He stood and shook Powell's hand.

"You did your best," he said. "You didn't do anything wrong."

In the program's final weeks, Powell and the other men were told to write a letter of apology or reconciliation as a way to finally find self-forgiveness. Powell addressed his to the little girl's parents. He'd never met the couple or knew if they survived the bombing, so the letter went nowhere. But it helped to put down the words and read them aloud to his fellow veterans.

"I want you to know," he wrote, "your daughter has been in my heart each day since that night."

___

A year ago April, Powell left OASIS with new tools and hope and friends he could lean on.

He was honorably discharged from the Army last August, and found work as a nurse at a home for the elderly in Crescent, but he realized he no longer had it in him to do the job he once loved. He quit and is pursuing a degree in industrial engineering.

He spends much of his time on his farmland, in his family since his great-great-grandmother arrived in Oklahoma to start a new life after being freed as a slave. Sometimes, he talks to God as he clears the brush around the walnut trees.

"I feel peace, redemption when I talk to him out there," he says. "I know he forgives me."

Powell has finally forgiven himself, too, but he knows he's not entirely healed.

He still takes medication for anxiety, depression and insomnia. But more than anything, he leans on the seven veterans. Their cellphones have become a lifeline, with daily texts.

Often Powell, the group's oldest member, is the one giving the advice. Helping them helps him, because he sees that he can still heal others.

The AP shared with Powell the medical experts' opinions that the girl's injuries likely caused her death. Said one, Bruce Goldberger, professor of toxicology at the University of Florida College of Medicine: "What he did probably was relieve the pain like they do in hospice care."

Hearing that brought relief for Powell. "It's something I've been carrying on my back for so many years, that guilty feeling," he says.

The girl still comes to him in his dreams. Not long ago, he envisioned her running through a pasture, and he yelled at her not to leave.

But he can put a distance between who he is now, and what happened then. And when his heart races and the anxiety returns, he stops to remind himself that he's not a bad person; it was just a bad situation.

"It will never go away," he says. "Now, I know how to deal with it."