The driver in the deadly Jan. 1 ramming attack in New Orleans visited the city twice in the months before he armed himself with guns and explosives and plowed a rented truck into a crowd on Bourbon Street, investigators said on Sunday.

In one visit in October, he cruised through the city’s French Quarter wearing glasses with a built-in camera, recording video images of the layout and atmosphere of the area, which is often packed with tourists.

Investigators have been pushing to piece together a clear timeline of the attacker’s actions, including a beat-by-beat accounting of his movements in the hours immediately before the attack. They have also mounted a far more sprawling search, looking back years, to understand his path to radicalization and how he planned and carried out the burst of violence that killed 14 people, injured many others and left New Orleans anguished and alarmed.

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.

The attack ended when the driver, Shamsud-Din Jabbar, a 42-year-old Army veteran from Houston who had a lucrative job with an international accounting firm, was killed in a shootout with police officers.

Mr. Jabbar had expressed allegiance to the Islamic State terrorist group, better known as 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.”