It was just after 3 a.m. on Wednesday, and while much of the country had already gone to bed after toasting the new year, the party was still going — as it usually does — on Bourbon Street in New Orleans.

Then came the roar of a white pickup truck, accelerating. In an instant, the city’s best-known, most popular public space was transformed into a scene of death and terror.

“We heard him punch the gas and then the impact and then the screams,” said Kimberly Stricklin, of Mobile, Alabama, who watched with her husband as the truck careened onto Bourbon Street and slammed into the crowd. “It just took a moment to register, it was just so frightening — it was like something out of a horror movie.”Stricklin said she was haunted by the memory of the sounds one victim had made. “I can’t get over that girl’s screams,” she said.

Described by federal authorities as a deliberate act of terror, the attack killed at least 15 people, wounded 30 and left New Orleans, a city of 364,000, on edge, after investigators said at a news conference Wednesday that they believed that the driver did not act alone.

The driver, who was killed in a shootout with police, was identified by the FBI as Shamsud-Din Bahar Jabbar, 42, a U.S. citizen and U.S. Army veteran from Texas. He had loaded his rented truck with weapons and at least one “potential” improvised explosive, authorities said, and an Islamic State group flag was found on the trailer hitch of his rented white Ford pickup.

As law enforcement officers swept through the French Quarter searching out suspicious packages and other potential threats and evidence on Wednesday, authorities urged the public to send tips to aid in the investigation, and vowed to track down everyone involved in the attack.

“We have a plan, we know what to do, and we will get these people,” Anne Kirkpatrick, the New Orleans police superintendent, said at a news conference Wednesday afternoon.

For residents watching events unfold, the day felt both frightening and surreal. Brian O’Brien, 57, a tour guide who lives a block from Bourbon Street, said he woke up on Wednesday to find a state trooper inspecting a cooler about 100 feet from his stoop. According to O’Brien, the officer said the cooler contained pipes, tape and lots of nails, and a bomb squad arrived soon after and detonated the contents.

O’Brien recalled hearing the squad shout, “Fire in the hole!” while he sat, with his ears covered, at a safe distance. “I’m still in shock,” he said in an interview.

Two officers were injured as police exchanged gunfire with the suspect after he had crashed and exited his truck; both officers survived.

The Sugar Bowl, part of the new 12-team college football championship, had drawn tens of thousands of spectators to New Orleans and was scheduled to be played Wednesday night at the Caesars Superdome, less than a mile from Bourbon Street. It was postponed until Thursday in the wake of the attack.

The attack happened near the intersection of Bourbon Street and Canal Street, on one of the busiest blocks in New Orleans, on one of the busiest nights of the year. Witnesses said the white pickup truck had careened around the corner from Canal Street onto Bourbon Street, easily breaking through or evading whatever modest barriers stood in its way.

Security barriers in the area, designed to protect Bourbon Street pedestrians from vehicles, were being upgraded; according to a notice on the city’s website, construction work to remove old bollards and install new, stainless-steel replacements began in November, and was scheduled to continue into February, in preparation for the Super Bowl, scheduled to be played in New Orleans next month.

City officials said Wednesday that the new bollards were not operational at the time of the attack, and that the suspect drove onto the sidewalk, avoiding a police car parked in the road.

Stricklin and her husband said that the only obstacle for the accelerating pickup had been a simple police barrier of thin poles. “It was just flimsy,” Kimberly Stricklin said.

The suspect, a Texas native, had converted to Islam, a man who had married his ex-wife said, and had acted erratically in recent months. Records showed that he had been married twice, and reported financial problems to his ex-wife’s lawyer in 2022.

Attorney General Merrick Garland said federal investigators were treating the attack as an act of terrorism. The use of the truck as a weapon, along with the discovery of an improvised bomb in a cooler near the crashed vehicle, led officials to conclude that the driver’s goal was to inflict civilian casualties.

“My heart is broken for those who began their year by learning people they love were killed in this horrific attack,” Garland said. He vowed to “deploy every available resource” to the investigation.

A compact neighborhood, just six-by-13 blocks, tucked along the curving bank of the Mississippi River, the French Quarter is famous for its distinctive architecture, ornate balconies, European flair and late-night party scene. Vibrant festivals on Bourbon Street, where the attack took place, attract revelers from around the world.

“You’re talking about one of the most iconic cities, and one of the most recognizable streets in the world,” Oliver Thomas, a New Orleans City Council member, said Wednesday after the attack. “So when you think about it, this isn’t really a message and a shot at New Orleans. This is at America.”

Video clips posted by witnesses on social media showed Bourbon Street emptied of crowds, who fled as the attack unfolded. Bodies of victims lay sprawled in the street, near gutters littered with empty cups and broken strands of colorful Mardi Gras beads. Stunned bystanders looked down from second-floor balconies.

The attack, by an assailant “set on hurting as many people as he could,” had targeted an area where crowds can be found at any hour, said Jason Williams, the district attorney who represents New Orleans.

“New Orleans is a place that doesn’t close,” Williams said, adding: “There’s always people, there’s always people out.”

This year’s Sugar Bowl, between the University of Georgia and Notre Dame, had been expected to bring as many as 100,000 people to the city, organizers said.

A University of Georgia student was among those critically injured in the attack, the school’s president said in a statement. The president, Jere W. Morehead, did not disclose the student’s name but said he had spoken to the family.

New Orleans is also preparing to host the Super Bowl at the Caesars Superdome on Feb. 9, another event expected to attract hundreds of thousands of visitors to the city.