Months before the man behind the New Orleans terror attack plowed a truck into a New Year’s Day crowd, he rode through the area on a bicycle, recording videos of his target using eyeglasses with a built-in camera, investigators said on Sunday. He was back again a few weeks later, they said, probably to continue his plotting.

Those details emerged as investigators revealed more about the driver and the extensive planning behind the attack, which killed 14 people, injured many others and left New Orleans starting 2025 grappling with a cascade of anguish and alarm.

Investigators have been pushing to piece together a clear timeline of the attacker’s actions. The investigation has entailed establishing a beat-by-beat accounting of his movements in the hours immediately before the attack, which included loading guns in his rented pickup truck and planting explosive devices in coolers near the site of the attack, Bourbon Street in the city’s French Quarter.

A far more sprawling search is looking back years to try to understand how a 42-year-old Army veteran with a lucrative job at an international accounting firm came to be radicalized, claiming alignment with the Islamic State terrorist group, better known as ISIS.

Investigators found that the attacker, Shamsud-Din Jabbar, had made trips to Egypt and Canada in 2023. But they said on Sunday that they had yet to determine what role, if any, those travels might have played in his evolving beliefs or his planning for the New Orleans attack.

“Our agents are getting answers as to where he went, who he met with and how those trips may or may not tie into his actions here in our city,” Lyonel Myrthil, the special agent in charge for the F.B.I. in New Orleans, said at a news conference.

New Orleans has been immersed in grief since the attack, but also marching forward, reopening Bourbon Street to the public and preparing to host the Super Bowl next month, as well as the season of celebration that precedes Mardi Gras. A crowd gathered on Bourbon Street on Saturday evening for a vigil that included a traditional second line. President Biden is scheduled to visit New Orleans on Monday.

”I believe only the power of prayer and faith in God can pull them and us through this time,” Gov. Jeff Landry, Republican of Louisiana, said on Sunday, referring to the pain the families of the victims and the community as a whole were navigating.

The attack ended when Mr. Jabbar, was killed in a shootout with the police that left two officers wounded. Officials praised the police for a swift response that they credited with sparing the city from more carnage.

Mr. Jabbar expressed allegiance to ISIS after a transformation that perplexed and troubled those who knew him. He had the group’s flag on the rented Ford F-150 pickup truck that he used in the attack. In a video that he recorded for his family, he said, “I wanted you to know that I joined ISIS earlier this year.”

Officials said on Sunday that they continue to believe Mr. Jabbar acted alone in carrying out the attack, and that they were still trying to determine whether he had deeper ties to ISIS. It remained unclear why he chose New Orleans as his target, officials said.

Christopher Raia, an F.B.I. counterterrorism official, said that individuals like Mr. Jabbar — who typically are radicalized online, use easily accessible weapons and act alone or in small clusters — were perhaps the “greatest terror threat” the country faces.

“They are difficult to identify, investigate and disrupt,” he said at the news conference on Sunday.

Investigators were also trying to find out where Mr. Jabbar went and what he did when he visited New Orleans in November, the second pre-attack visit that officials are aware of. The first visit, when he recorded the video images from a bicycle, took place in October.

Investigators discovered that he had left two improvised explosive devices in coolers at nearby locations shortly before ramming his truck into the Bourbon Street crowd early on New Year’s morning. They said he appeared to have had limited experience in building and using explosives, and the devices he created were crude, but they believed some of them could have been effective.

Mr. Jabbar had a transmitter in the rented pickup. “We believe that the transmitter would have functioned,” Mr. Myrthil said.

One of the coolers had been moved from where Mr. Jabbar had placed it, officials said, but the people who moved it were “unknowing Bourbon Street visitors” who had no connection to Mr. Jabbar.

Both devices were deactivated by the authorities shortly after the ramming attack.

Investigators said Mr. Jabbar had rented the pickup weeks before the attack, and drove it to New Orleans from his home in Texas, arriving on the afternoon of Dec. 31. Investigators found bomb-making materials at a residence he had rented in New Orleans, where he had set a fire just before setting off for the French Quarter. Officials said the fire burned itself out within a few hours and was already extinguished by the time firefighters arrived at the home.