Former Army Maj. Ian Fishback, a U.S. Military Academy graduate and combat veteran whose condemnation of torture by U.S. soldiers in Iraq produced groundbreaking legislation in the early years of that war, died Nov. 19 at an adult foster-care facility in Bangor, Mich. He was 42.

His father, John Fishback, said the cause had not been determined but that Maj. Fishback, who served in the military until 2015, had been racked by paranoid and delusional thoughts for months. He speculated that his son’s experiences in combat may have caused a neurological degeneration that contributed to his erratic behavior.

During his years in the military and long after, Maj. Fishback developed a reputation for uncompromising moral courage. Upon returning in 2005 from a tour in Iraq with the Army’s 82nd Airborne Division, he wrote a letter decrying the abuse of Iraqi detainees by his unit. He sent it that September to Sen. John McCain (R-Ariz.), who had endured more than five years of imprisonment and torture by the North Vietnamese as a young naval officer, and to Sen. John W. Warner (R-Va.), the chairman of the Senate Armed Services Committee.

Maj. Fishback said vague, contradictory and inconsistent guidance from Defense Secretary Donald H. Rumsfeld and senior military leaders had led to a “wide range of abuses” by U.S. soldiers in Iraq and Afghanistan, including “death threats, beatings, broken bones, murder, exposure to elements, extreme forced physical exertion, hostage-taking, stripping, sleep deprivation and degrading treatment.”

Maj. Fishback, who also did combat tours with the Army’s 5th Special Forces Group, wrote that it was his responsibility as an officer to ensure that his men “would never commit a dishonorable act.”

“It absolutely breaks my heart that I have failed some of them in this regard,” he wrote in his letter.

Two additional 82nd Airborne Division soldiers buttressed and expanded on the allegations of abuse in a report released by Human Rights Watch shortly after Maj. Fishback sent his letter to McCain and Warner. Within weeks, the Senate voted 90 to 9 to approve the Detainee Treatment Act, which mandated “no individual under the physical control of the United States Government, regardless of nationality or physical location, shall be subject to cruel, inhuman, or degrading treatment or punishment.”

As one of the military’s most prominent active-duty whistleblowers, Maj. Fishback helped to reorient interrogation and detainee policy amid the fear and paranoia of the 9/11 terrorist attacks. “Some argue that since our actions are not as horrifying as al-Qaeda’s, we should not be concerned,” he wrote in his 2005 letter. “When did al-Qaeda become any type of standard by which we measure the morality of the United States?”

Maj. Fishback’s stand led Time magazine to name him of its 100 most influential people in the world that year and compare his actions “to helicopter pilot Hugh Thompson’s heroism that ended Vietnam’s My Lai Massacre.”

Ian Fishback was born in Detroit on Jan. 19, 1979. His parents were rural mail carriers, and John Fishback was also a combat veteran, serving with the Marines in Vietnam from 1966 to 1967. “I came back from Vietnam and I had some problems, but I was saved by the peace movement,” his father said.

Maj. Fishback’s childhood home was full of antiwar posters bearing slogans such as “War is not healthy for children and other living things.”

A high school teacher suggested that Ian Fishback, who excelled academically and athletically, apply to a service academy. He graduated in 2001 from the U.S. Military Academy at West Point, N.Y., and in 2012 received a master’s degree in philosophy and political science from the University of Michigan.

In addition to his combat assignments, Maj. Fishback taught philosophy and just war theory at the U.S. Military Academy. “His intensity made for a distinct classroom experience,” Theo Lipsky, an Army captain who studied under him, wrote in an essay posted on the academy’s Modern War Institute website.

“His lessons were that meaningful philosophical inquiry separated an officer from a mere killer,” Lipsky wrote, and that cadets “had to ask by what right and with what consequence might they one day kill.”

His marriage to Clara Hoisington, a fellow West Point graduate, ended in divorce. In addition to his father, of Newberry, survivors include a daughter, Dresden Fishback of Burlington, Iowa; his mother, Sharon Ableson of McMillan, Mich.; a stepmother, Sharon Brown of Newberry; and a sister.

Earlier this year, Maj. Fishback completed his doctorate in philosophy at the University of Michigan. His thesis on the “Method and Morality of War” explored the moral and legal responsibilities of commanders and combatants in battle.

Maj. Fishback’s academic colleagues said his work was animated by his intellect as well as the experience of having fought in places such as Iraq and Afghanistan, where it was often difficult to distinguish friend and foe and where soldiers were under intense pressure to make split-second life-or-death decisions.

Maj. Fishback left the Army and then his country deeply disillusioned. “I gave the U.S. a lifetime of service — very admirable service. And if this is the repayment, it is not acceptable,” he told his hometown Newberry News in January as he was preparing to leave the country and apply for European Union citizenship.

He moved to Sweden on a Fulbright scholarship but soon became overwhelmed by delusions that secret U.S. government teams were tracking and planning to imprison or kill him. A months-long effort to get Maj. Fishback care from the Department of Veterans Affairs was stymied by bureaucratic roadblocks and inertia, his family said.

Maj. Fishback’s aggressive behavior alarmed law enforcement in Newberry, leading to court-mandated treatment. For several months he cycled through halfway houses and state-funded psychiatric facilities as his friends pushed to get him into a VA hospital in Battle Creek, Mich.

A GoFundMe campaign, initiated by several of Maj. Fishback’s oldest friends, sought to raise $60,000 to transfer him from the group home to a private psychiatric treatment facility where he could receive care until a VA bed opened for him.

Nancy Sherman, a philosophy professor at Georgetown University who befriended Maj. Fishback, said that his “unswerving moral rectitude” made him an exceptional soldier and academic but that in recent years he was overcome by paranoia that fellow academics were plagiarizing him and undermining his work.

“He lived what he believed,” Sherman said. “And that sense of morality and sense of moral consciousness that did this country so much good also had its costs. This is a guy who served remarkably courageously. … He’s a flawed, tragic hero.”

Alex Horton contributed to this report.