‘I Joined ISIS’: The New Orleans Attacker’s Secret Radicalization

His electric truck was already headed toward New Orleans, traveling from his trailer home outside Houston and past the twinkling oil refineries to the east, when Shamsud-Din Jabbar began capturing a video on his phone in the dark.

“I wanted to record this message for my family,” Mr. Jabbar said. “I wanted you to know that I joined ISIS earlier this year.”

Mr. Jabbar then added a chilling addendum.

“I don’t want you to think I spared you willingly,” he said, according to details of the video reviewed by The New York Times. He told his family that he had previously conceived of organizing a “celebration” for them and then making everyone “witness the killing of the apostates.”

The words were among Mr. Jabbar’s last before he plowed his rented pickup truck through early morning New Year’s crowds on Bourbon Street in New Orleans, killing 14 people before dying in a shootout with the police. He carried with him in the truck the flag of the Islamic State terrorist group, better known as ISIS.

The devastating violence revealed a secret radicalization that confounded his loved ones, who knew him as a decorated Army veteran who held a $120,000-a-year job as a “senior solutions specialist” focused on government and public services at the international accounting firm Deloitte. Days later, investigators were still trying to trace exactly how Mr. Jabbar had managed to descend into such a murderous state without detection.

But new details from recordings, interviews and public records trace Mr. Jabbar’s growing discontent with American society and a shift toward what was at first a more conservative version of Islam, and then something much darker.

Much of the scrutiny is on the past year, when Mr. Jabbar deepened his isolation from others as he moved into a Muslim neighborhood just north of Houston, a cluster of mobile homes where chickens, goats and cats roam freely through backyards.

Even as he found himself surrounded by fellow believers, in a community situated within walking distance of one mosque, and a short drive from a second, he remained an outcast, several neighbors said.

He holed up alone in his home, keeping visitors away and limiting contact with neighbors. A neighbor recalled that Mr. Jabbar had grown his beard long and then cut it short again.

Several residents said they had never seen him at prayers at the nearest mosque, and the spokesman for the one farther away also said he did not remember him attending.

“We’d never seen him here worshiping in our lives, and I’ve been in this community since 2008,” one local resident, Taha Mohamed, said as he attended a prayer service Thursday evening.

Mr. Jabbar did not discuss his growing hard-line religious beliefs with those around him, his neighbors said, even as he occasionally posted audio recordings espousing a conservative interpretation of Islam.

At Mr. Jabbar’s house, there were signs of a dual life. On his patio, the man who had worked for years in real estate and information technology had left behind several real estate yard signs. Inside, a laptop sat on a workstation with two monitors, and a bookshelf contained both the Quran and a book about Christianity.

Investigators wrote in documents of finding more ominous items that Mr. Jabbar had left behind, including supplies that could be used for an explosive device: acetone, bottles of sulfuric acid and bags labeled as potassium nitrate.

The military ‘grounded him’

At the three-bedroom home in Beaumont, Texas, where Mr. Jabbar grew up, family members gathered this week and looked through photos of his life that showed him smiling in his Little League gear and in a flowing red graduation gown and cap.

Mr. Jabbar had what seemed to be a relatively ordinary upbringing, said Abdur Rahim Jabbar IV, a 24-year-old half brother. He loved school and got good grades.

Mr. Jabbar’s father grew up as Christian but later turned to Islam, changing his last name from Young to Jabbar and also giving some of his children Arabic names. Still, many members of the family, who are all African-American, continued attending a local Baptist church.

A relative of Mr. Jabbar’s, who did not want her name published for fear of being drawn into the case, said that even Mr. Jabbar and some of his brothers, who like their father converted to Islam, had lived largely secular lives. “I don’t think I ever heard the word Allah said,” she recalled.

Mr. Jabbar’s mother, who remained a Christian, later moved with Shamsud-Din and the couple’s other children to the Houston area after the divorce.

At the University of Houston, Mr. Jabbar took in the college experience. He enjoyed college parties and alcohol so much, his half brother said, that it derailed his academics and eventually cost him a scholarship.

By 2007, he had joined the U.S. Army, eventually working in both human resources and information technology, rising to the rank of staff sergeant, being deployed to Afghanistan and earning a Global War on Terrorism service medal. The Army featured him in a 2013 post on Facebook. There, Mr. Jabbar’s mother replied with a comment, expressing her pride.

Mr. Jabbar told family members that he was grateful for his time in the military. “It set him straight,” his half brother said. “It gave him some discipline. It grounded him.”

After eight years of service, Mr. Jabbar attended Georgia State University. People who knew him still saw no signs of religious extremism, though at least one friend described a growing interest in his Muslim faith.

He then turned to a white-collar professional career and returned to Texas.

‘A sign of the end times’

Mr. Jabbar’s personal troubles at first appeared in more worldly forms. There were divorces and business troubles and disputes over finances.

With the marital separations came alimony and child support for his two daughters, now ages 20 and 15, and his young son. In 2021, court records from his third divorce show that he was ordered to pay $1,350 a month to his third wife. He was working in real estate with his relatives to earn extra income, in part because of debts: The house involved in his divorce case was facing foreclosure, he reported in 2022, with $27,000 in back payments owed on the mortgage.

By the time that divorce was finalized in 2022, he had the job at Deloitte, but appeared to be paying over a quarter of his monthly salary in such support.

His third divorce appeared to be a bitter one in which his ex-wife asked the court to order Mr. Jabbar not to make threatening phone calls or harm either her or their son. It was not clear if he had ever harmed them in the past. His ex-wife declined requests for comment.

Over the past year, Mr. Jabbar appeared to some in his family to have begun acting erratically. A previous ex-wife and her husband moved to limit his contact with their children as his behavior grew more unpredictable, seemingly influenced by his religious views, the husband said.

Mr. Jabbar’s closer family also saw signs that he was beginning to unravel, in part as a result of financial stress and divorce, but also of larger things in the world. After the war in the Middle East began in the fall of 2023, Mr. Jabbar seemed uneasy with the carnage he saw on the news and social media, said his half brother, Abdur Jabbar.

“He didn’t like it — he said it was genocide on both sides, inhumane,” he said. “It was senseless.”

In the past year, Mr. Jabbar began growing a beard, which some family members shrugged off as an attempt to change his look and adopt the look of a traditional Muslim man. But he also began expressing disgust over what he saw as inappropriate behavior.

“He didn’t approve of drinking or partying,” his half brother said. “He said it was not in accordance with what God commanded us to do. He said it wasn’t fruitful. He said it didn’t bring anything positive.”

Recordings about Islamic teachings were posted to an account on the audio website SoundCloud that appears to belong to Mr. Jabbar; the voice was verified by his half brother. In one of them, he warned that music had the power to lure people “into the things that God had made forbidden to us,” such as alcohol, marijuana, vulgarity and crime.

The recording goes on to suggest a connection between the release of “Get Rich or Die Tryin’,” a rap album by 50 Cent, and a series of murders in his neighborhood. He said he worried that Muslims listening to such music were being drawn into evil.

“And the voice of Satan spreading among Prophet Muhammad’s followers — peace be upon him — is a sign of the end times,” he said in the message about a year ago, in early 2024.

‘The believers and the disbelievers’

His recordings reflected a growing conservatism in his beliefs. But investigators were still poring over his digital life to determine when he had made the jump to extremism and why, in the videos he recorded and posted to Facebook just before the attack, he had pledged himself to ISIS.

Nasser Weddady, an expert on Islamic extremism, said the views contained in the SoundCloud recordings showed a puritan bent but were not associated with a violent interpretation of the faith on their own.

The same SoundCloud account also included 16 other recordings that the user had “liked,” several of which expressed views about Islam that have sometimes been used by extremist groups as justification for killing non-Muslims.

The bigger question, Mr. Weddady said, “is how did he go from blaming Muslims for straying from the straight path, to killing non-Muslims?”

Abdur Jabbar said that when he had spoken to his half brother two weeks ago, Mr. Jabbar did not mention any plans to go to New Orleans.

At his Deloitte job, he set an out-of-office reply saying that he was taking some personal time off.

“Please expect a delay in response during this time,” the message said. “If the matter is time sensitive, please call or text me.”

“Thanks kindly,” he concluded.

Neighbors said Mr. Jabbar’s lease outside Houston was coming to an end and that he had told them before he departed on New Year’s Eve that he was moving to New Orleans.

After renting the truck on a peer-to-peer rental app, Mr. Jabbar headed for New Orleans, recording video messages along the way. In the first video, he referred to “animosity” with his family but said that he had decided not to follow through on a plan to harm them. Investigators said this was apparently because of a concern that news coverage of an attack that involved his family would not focus on the “war between the believers and the disbelievers.”

He started posting his videos at 1:29 a.m. and continued until 3:02 a.m. His attack began just minutes later.

A U.S. official who reviewed some of the footage filmed by Mr. Jabbar said that he “pledges bayat” to the Islamic State, an Arabic term referring to the oath of loyalty that ISIS followers are expected to pronounce as a way to signal their allegiance to the group.

Mr. Jabbar’s brother said he had not seen the videos addressed to the family.

“It’s just hard to believe — it’s insane,” he said. “It’s unlike him.”

On Thursday afternoon, Abdur Jabbar pushed a wheelchair carrying his ailing father, who had suffered a stroke in 2022, to the home’s garage to meet with three F.B.I. agents. The agents told the family, Abdur Jabbar said, that there were red flags showing that Shamsud-Din Jabbar had been radicalized.

“They want to know why he did this,” the younger Jabbar said after the F.B.I. questioning. “I could not give them an answer. That’s not the brother I know.”

Mr. Jabbar’s religious influences remained unclear.

The two mosques in his small neighborhood represent two distinct interpretations of Islam. One, the Baitus Samee Mosque, has come under criticism from more conservative Muslims, some of whom have branded the mosque’s followers as “apostates.” When graffiti to that effect was sprayed on a wall of the mosque in August, the F.B.I. posted a $10,000 reward, hoping to make an arrest.

The other mosque, known as the Bilal Mosque, closest to where Mr. Jabbar lived, has drawn attention of its own, as on at least one occasion, it hosted a speaker who made inflammatory remarks denouncing Jews.

Congregants said they had not seen Mr. Jabbar at either one.

On Friday, as residents gathered at the Bilal mosque for afternoon prayers, several constables, sheriff’s deputies and private security guards stood watch.

Many who lived in the area said they worried about the new attention brought to their community and were frustrated that they were now being connected to Mr. Jabbar simply because he had lived, in the last months of his life, just down the street.

“He wasn’t a member of this congregation, he wasn’t someone that used to come here, and he had no part in this community whatsoever,” said Mohammed Khan, a member of the Bilal Mosque. Online anti-Muslim vitriol since the attack has only deepened their concerns, he added.

Inside the mosque, Ayman Kabire of the Islamic Society of Greater Houston, who served as the imam on Friday, condemned Mr. Jabbar’s attack, reminding those gathered that their faith was rooted in peace.

Outside, a helicopter that appeared to be watching the gathering below circled overhead, drowning out conversations.

Mike Baker, J. David Goodman, Nicholas Bogel-Burroughs, Maria Jimenez Moya, Shannon Sims and John Ismay contributed reporting. Kirsten Noyes, Sheelagh McNeill, Susan C. Beachy and Alain Delaquérière contributed research.