LAURA BARRON-LOPEZ: Welcome to the "News Hour."

At least 15 people are dead and dozens injured after a man driving a truck barreled through the French Quarter in New Orleans early this morning, where people had gathered to usher in the new year.

Authorities found an ISIS flag and weapons in the truck.

The suspect, a U.S.-born citizen, is dead, and the FBI is investigating the attack as an act of terrorism.

A warning: Video of the attack is disturbing.

In New Orleans, what should have been a night of celebration ringing in the new year ended in terror.

Authorities say, at around 3:15 a.m., the suspect plowed a white Ford pickup truck into a crowd on Bourbon Street.

After crashing the vehicle, the driver fired at police officers on the scene.

Law enforcement intervened, killing the man, identified today as 42-year-old Shamsud-Din Jabbar,all of this leaving an unimaginable trail of destruction and lifeless bodies in the streets.

Today, a coroner van on the city's main roads, a popular area known for its bars and live music, now an active crime scene.

More than 30 people were injured, including two police officers shot that remain in stable condition.

Witnesses describe the scene as surreal.

MAN: What we saw was insanity, I mean, something out of a movie, the graphic nature of it, and it was unbelievable.

LAURA BARRON-LOPEZ: Authorities say he was dressed in military gear and had an ISIS flag inside the vehicle.

New Orleans Police Superintendent Anne Kirkpatrick: ANNE KIRKPATRICK, New Orleans, Louisiana, Police Superintendent: Because of the intentional mind-set of this perpetrator who went around our barricades in order to conduct this, he was hell-bent on creating the carnage and the damage that he did.

LAURA BARRON-LOPEZ: The FBI does not believe the suspect acted alone and is asking the public for help.

ALETHA DUNCAN, FBI Special Agent: We're asking if anyone has had any interaction with the deceased subject, Jabbar, in the last 72 hours, provide us with this information.

LAURA BARRON-LOPEZ: President-elect Donald Trump implied the attacker was an immigrant, saying -- quote -- "When I said that the criminals coming in are far worse than the criminals we have in our country, it turned out to be true."

But authorities confirmed the suspect was a U.S.-born citizen from Texas and an Army veteran.

New Orleans Mayor LaToya Cantrell told residents her priority is safety.

LATOYA CANTRELL, Mayor of New Orleans, Louisiana: The mission now is to facilitate, support, and coordinate safety procedures to keep our residents and our visitors safe.

We're taking every necessary step to put even more safety procedures in place, especially given the nature of the investigation.

LAURA BARRON-LOPEZ: Increased police presence can be seen around the area as the investigation continues.

The Sugar Bowl college playoff, initially scheduled for tonight just blocks from the attack, has been postponed until tomorrow.

For insight into the ongoing terrorism investigation, we're joined by Bruce Hoffman, senior fellow for counterterrorism and homeland security at the Council on Foreign Relations.

He's advised the CIA and has studied terrorism and insurgency for five decades.

Bruce, thank you so much for joining us this evening.

The suspect was an Army veteran and he had an ISIS flag in his truck, according to authorities.

How significant is it that he had that ISIS flag and what else stands out to you?

BRUCE HOFFMAN, Council on Foreign Relations: The ISIS flag is enormously significant, because it's very clear he was trying to situate this act of violence in a political context, indeed in a terrorist context, and show allegiance or support of ISIS' aims.

LAURA BARRON-LOPEZ: Law enforcement has said that they don't believe that the suspect, Shamsud-Din Jabbar, was acting alone.

So what can we infer so far from what we know about who else might be involved or what this means?

BRUCE HOFFMAN: This is what's so alarming about this particular incident is, it wasn't just a matter of someone getting in a truck and driving from Texas to Louisiana and carry out an attack.

It's believed that at least two other improvised explosive devices were found in the French Quarter of New Orleans and that several other men and a woman have been captured on video planting them there.

So this suggests some conspiratorial dimension to the attack, which means that this may not be isolated.

LAURA BARRON-LOPEZ: Right.

Authorities did say in the last few hours, though, that they're not sure if that man and woman were involved or connected to the suspect, but there's a lot that we still don't know.

And, again, based on the information that we have so far, how likely is it that the suspect was inspired or directly linked to ISIS?

BRUCE HOFFMAN: It's difficult to say.

It's clear that he was going through some personal crisis.

He had financial problems, for example.

He was recently divorced.

He's a recent convert to a religion, for example.

All of those things may have played in his mind of doing something daring, dramatic and violent that would all of a sudden catapult him into some sort of infamous notoriety, but notoriety nonetheless, as opposed to having been a failure at everything else that he's tried.

And what we know from the recruitment and radicalization of individuals is that members of terrorist organizations, handlers play on individuals' personal weaknesses or their personal traumas and attempt to get them to engage in acts of violence that, in normal circumstances, they might never have contemplated.

LAURA BARRON-LOPEZ: Are there similarities between this attack, between what we know about the suspect, and past U.S.-grown acts of terrorism that may or may not have been linked to ISIS?

BRUCE HOFFMAN: Well, we really have to put this in a broader context.

ISIS, for at least the past decade, has deliberately targeted highly populated, let's say, celebratory type of events, the Ariana Grande concert in Manchester, England in 2017.

For instance, just this past summer, there was an attempted attack on the Taylor Swift concert in Vienna, Austria.

So, ISIS has generally in recent years been striking at events where there's densely populated and, as it's well-attended, they're celebrating something, whether it's a concert or, as in this morning's tragedy, a New Year's Eve event, and trying to find places where they can kill lots of people, but also get lots of attention.

LAURA BARRON-LOPEZ: ISIS has been substantially weakened in recent years, but what reasons would they still have to attack the U.S.?

BRUCE HOFFMAN: Well, one of the main reasons is that, during the Trump administration, for example, on several occasions, President Trump proclaimed the defeat of ISIS, which was in fact the case.

The international campaign against ISIS from 2014 to 2019 destroyed the caliphate.

This could be a way of ISIS poking at the United States, especially as the inauguration is only three weeks away.

LAURA BARRON-LOPEZ: I mean, could this attack indicate that ISIS might still have more influence than we previously believed and the ability to conduct an attack like this on U.S. soil?

BRUCE HOFFMAN: Absolutely.

Let's not forget that there was an aborted ISIS plot that was derailed in October to stage an attack in Oklahoma City on Election Day.

So, unfortunately, we have to see this morning's events as not necessarily an aberration.

LAURA BARRON-LOPEZ: Bruce, what are you looking for as the investigation moves forward?

BRUCE HOFFMAN: I think the biggest question is, was this a broader conspiracy and who are the fellow conspirators and what conceivably might be next?

I would say, secondly, it's whether that explosion, a very mysterious explosion of a Cybertruck outside of a Trump-owned hotel in Las Vegas is in any way connected to this event as well.

It seems odd that two electric vehicles are involved in explosions on the same day.

LAURA BARRON-LOPEZ: Bruce Hoffman, thank you so much for your time and your insights.

BRUCE HOFFMAN: You're very welcome.