US Army officer-turned-terrorist thought Fort Hood attack would save mother's soul, letters show Hasan hoped to balance what he saw were his own mother's sins.

Newly published excerpts of jailhouse letters from U.S. Army officer-turned-terrorist Nidal Hasan show that he is almost completely without remorse for the 13 lives he took during the Fort Hood attack in 2009, the culmination of a twisted jihadist quest that he hoped would somehow save his mother’s soul.

Asked if he believed he was committing a “good deed” by murdering his fellow soldiers that day, former Army Maj. Hasan responded in one letter to a terrorism researcher, “Of course!”

“I considered those who were trying to help the U.S. undermine the Taliban’s attempt to establish Sharia (God’s) Law as the supreme law of the land and replace it with something else like a democracy that doesn’t rule by God’s law the enemies of God, and thus worthy of fighting/killing,” Hasan wrote in a letter to the researcher Katharine Poppe in November 2017, portions of which were published by the George Washington University’s Program on Extremism on Thursday.

In doing this “good deed,” Hasan hoped to balance what he saw were his own mother’s sins — namely selling alcohol for years at their secular Muslim family’s store — to save her from literally burning for all eternity.

In a new study Poppe, a relative of one of Hasan’s former defense attorneys, traces Hasan’s life from his birth in 1970 in Virginia, through his Army training and his slow embrace of violent radical Islamic ideas. It identifies the 2001 death of his mother as a spiritual and psychological breaking point, eight years prior to the Ft. Hood massacre and more of an influence on his actions than his much-reported correspondence years later with Al Qaeda preacher Anwar al-Awlaki.

“There’s usually some trigger event which causes somebody to go down that path,” GWU Program on Extremism Deputy Director Seamus Hughes told ABC News. “His mother’s death was one of them – it was the event.”

Before Hasan’s own radicalization, his family was moderate, and his parents ran a convenience store that sold alcohol. When his mother became sick with cancer and later died, Hasan was overtaken by fear that the selling of alcohol was forbidden by the Qur’an and that she would therefore burn in hell.

“This religious interpretation was one he believed to be entirely literal – his mother would spend an eternity burning in a pit of fire,” the study said. “[But] her sins, as he saw them, could be outweighed by good actions he did on her behalf.”

Over the following years, Hasan devoted himself to the study of Islam and slowly attached himself to more and more radical interpretations — largely overlooked by the Army even as he became radicalized while attending a military medical school — until he convinced himself that he would have to undertake a dramatic attack on his fellow American soldiers in hopes of saving his mother.

During this period, the study also provides a more nuanced view on the role that Al Qaeda cleric Anwar al-Awlaki, who was killed in a CIA drone strike in Yemen in September 2011, may have played in Hasan’s radicalization.

Al-Awlaki happened to preside over Hasan’s mother’s funeral there, but beyond that the two had little contact. In fact, Hasan later said he didn’t realize Awlaki had been the voice of the fiery sermons Hasan listened to in his car as part of his religious “study.”

Hasan did reach out to al-Awlaki prior to the 2009 attack, but as investigators knew at the time behind closed doors, the email correspondence shows al-Awlaki barely responded to Hasan and did not encourage or advise him to carry out violent attacks. (Investigators were later criticized for not realizing the importance of Hasan’s side of the conversation, in which he asked questions about the religious justifications for violence.)

“The conventional wisdom is that al-Awlaki played an oversized role in Hasan’s decision-making,” Hughes said. But the study showed that in this case Hasan had already decided to act on his own and al-Awlaki was more like “the background noise.”

More troubling were what Hughes called the “numerous” warning signs about Hasan’s radicalization that the military and law enforcement missed, including multiple presentations during Hasan’s medical training in which he obsessed over a “War against Islam” he felt was being waged by the U.S.

The study said that by 2009 Hasan had already decided to commit some act of violence but wasn’t sure what to do. Then he got word he was being ordered to deploy to Afghanistan. Hasan said he decided that getting his orders from the U.S. military was really “a task from God to speed up his actions,” the study said, citing a sanity board report prepared during court proceedings later.

From then, Hasan’s only hesitation was over breaking the oath to protect and defend the U.S. Constitution he pledged when he joined the military – another sin. In the end, he went ahead anyway.

Hasan killed 12 soldiers and one civilian on Nov. 5, 2009, and wounded 32 others before he was shot, severely wounded and arrested.

While in prison Hasan fasted for a period of time, on the off chance that he was incorrect in his belief that his massacre was justified. But for the most part, he stood by his deadly attack.

Prior to being sentenced to death in 2013, the study said Hasan planned to apologize for his actions – but only for breaking his oath to the military. Hasan never read the statement in court.

“In his own words, he believed that what he had done was correct and that the people he had killed were religiously permissible because, in his mind, they posed a direct threat to Islam and his fellow Muslims in Iraq and Afghanistan,” the report said.

After his conviction and sentencing, Hasan was sent to a military detention center at Fort Leavenworth in Kansas, where he’s currently incarcerated.

Hughes said he hopes the study of Hasan’s life and radicalization will shed more light on the “lone attacker” and help counter-terrorism officials reevaluate how to defend against them.

“If you want to understand the phenomenon of lone actor attacks, one of the best places to start is to study Nidal Hasan and the attack at Fort Hood,” he said.

[CORRECTION: A previous version of this report misstated the location of Fort Leavenworth. This report has been updated to correct the error.]