Driver in 'Monstrous' Truck Attack Was Unknown to Security Officials

— -- The suspected terrorist who killed dozens of people -- including at least 10 children -- by plowing a truck into a crowd in France during Bastille Day celebrations Thursday night has been identified by officials as 31-year-old Mohamed Lahouaiej Bouhlel, who was unknown to French security services.

Bouhlel, who was born in Tunisia, lived in Nice with his wife and worked as a delivery driver, officials said. He was killed in a shootout with police from his 18-ton vehicle.

Nice attack remembered in photos

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During Bastille Day celebrations in 2016, a terrorist drove a truck into the gathered crowds in Nice, France, resulting in the deaths of 86 people. The driver, Mohamed Lahouaiej-Bouhlel, was a Tunisian living in France and was killed by police following the attack. ISIS claimed responsibility and then French President François Hollande ordered airstrikes in retaliation on ISIS militant locations in both Syria and Iraq. French police forces and forensic officers investigate a truck that ran into a crowd in Nice, France, on July 14, 2016.

Eric Gaillard/Reuters

Fingerprints confirmed Bouhlel's identity and his wife has been detained since this morning, French prosecutor Francois Molins said at a news conference today.

Officials recovered an automatic handgun, grenade and ammunition from his truck, among other weapons and items. Investigators seized computers and cellphones during searches at two different addresses, Molins said.

Although Molins said the man was "entirely unknown by intelligence services" and had no file of radicalization, Bouhlel was sentenced in March to a six-month suspended prison sentence for use of a weapon.

That case involved him and another motorist and the weapon was a piece of wood, officials said.

Two Americans were among the at least 84 killed in the attack, when the driver mowed down a large crowd with a truck hauling grenades and other weapons during Bastille Day celebrations in Nice, the U.S. State Department said.

Officials did not name the two Americans, although family members confirmed their identities to ABC News.

Sean Copeland and his 11-year-old son Brodie, who were in Nice on a family vacation, were killed in the attack, Alyssa Weaver, the elder Copeland's niece, wrote on Twitter. The Copelands are from Lakeway, Texas, about 30 miles west of Austin.

Weaver tweeted, "I am asking for prayers for my family, due to the tragedy in Nice, France I lost my uncle Sean and my 11 year old cousin Brodie I ask for prayers for my aunt Kim and my two other cousins Maegan and Austin during this tough time and prayers for my family’s safe trip back home #CopelandStrong”

Three UC Berkeley students studying abroad in Nice were injured in the attack, the university said. One student sustained two broken legs and another had a broken foot. Another UC Berkeley student, 20-year-old Nicolas Leslie, is still unaccounted for.

France's prosecutor said that in addition to those killed, including 10 children, more than 200 others were injured. Among them, 52 were in critical condition.

The driver was shooting out the window as he slammed his vehicle into crowds for over a mile along the Promenade des Anglais, officials said. He was shot by police while firing his gun through the window, they added.

Images of the truck showed the windshield riddled with bullet holes.

Witnesses described how a festive night watching fireworks on the seafront for the French holiday ended in horror.

Shortly after the fireworks ended, Inga Romanoff was walking down the promenade when she heard gunshots.

"I started running and I looked back and I saw the truck going through the people right in the place where I was standing. It was just seconds," Romanoff said on "Good Morning America" today. "I don't think people had any time to jump out of the way."

Chaos erupted as people tried to flee the driver's deadly path, Romanoff said.

A woman next to her stumbled and fell, she said. "People kept running over her, and I was trying to pick her up so she could also run."

It was complete chaos," she said. "People were running in different directions."

Sam Helwani, a French teacher from New Jersey, was with friends further from the scene when they saw a crowd running in their direction.

"It was like a mass exodus of people running towards us," Helwani told ABC News today. "I had asked a woman in French, what’s the problem? What’s going on? And she said there’s a man with a gun."

Helwani, who has traveled to Nice for the past six years, said he's still shaken up by what happened, but won't let it impact the rest of his trip.

"I still can't eat anything. I'm still a little shaky," he said. "I'm here until the end of August so I have a really long trip planned and I'm not going to stop doing what I do."

French President Francois Hollande extended the country's state of emergency, which was due to end this month, for another three months and was mobilizing reservists. He said it was unclear whether the attacker had any accomplices.

"France is horrified by what has just occurred -- a monstrous act of using a truck to intentionally kill dozens of people celebrating 14th of July," the French president said during a nationally televised address early today. "France is strong. France will always be stronger than the fanatics who want to strike France today."

Officials said there have been no claims of responsibility. The Paris anti-terrorism prosecutor's office was put in charge of the investigation.

Graphic images surfaced on social media showing the mayhem, including the truck barreling through crowds as dozens are seen running from the scene.

Pope Francis tweeted this morning that he was praying for the victims.

President Obama also issued a statement calling the incident a "horrific terrorist attack."

Secretary of State John Kerry, who joined French leaders Thursday at Bastille Day celebrations in Paris, said he would continue to stand "firmly" with the French people during this time.

French Prime Minister Manuel Valls said the government has declared three days of national mourning after the attack in Nice.

Vallas said the national mourning would begin Saturday.

ABC News' Louise Dewast contributed to this report.