By Brian Thevenot

NEW ORLEANS (Reuters) - Investigators in New Orleans were searching on Thursday for what motivated a U.S. Army veteran flying an ISIS flag from his truck to plow into a crowd of New Year's revelers, killing 15 people and injuring 30 more before dying in a shootout with police.

The probe was focused on whether the suspect, Shamsud-Din Jabbar, 42, a U.S. citizen from Texas who once served in Afghanistan, had help in planning the deadly attack on a city that will host the NFL Super Bowl next month.

FBI officials said they were also looking for any links between the deadly attack and a separate incident on Wednesday in which a Tesla Cybertruck exploded in flames outside the Trump International Hotel in Las Vegas, just weeks before President-elect Donald Trump returns to the White House on Jan. 20.

The New Orleans attack injured about 30 other people, including two police officers wounded by gunfire from the suspect, taking place a mere three hours into the New Year in the historic French Quarter.

The victims included the mother of a 4-year-old who had just moved into a new apartment after getting a promotion at work, a New York financial employee and accomplished student-athlete who was visiting home for the holidays, and an 18-year-old aspiring nurse from Mississippi.

Witnesses described a horrifying scene.

"There were people everywhere," Kimberly Strickland of Mobile, Alabama, said in an interview. "You just heard this squeal and the rev of the engine and this huge loud impact and then the people screaming and debris - just metal - the sound of crunching metal and bodies."

Meanwhile authorities vowed to continue to search for any evidence that Jabbar had accomplices.

One New Year's Day tradition - the classic college football known as the Sugar Bowl - was rescheduled for Thursday afternoon. Kickoff for the game between Notre Dame and Georgia was put off for nearly 24 hours while police swept parts of the city looking for possible explosive devices and converged on neighborhoods in search of clues.

The city will also host the NFL Super Bowl on Feb. 9.

Police found weapons and a potential explosive device in the vehicle, while two potential explosive devices were found in the French Quarter and rendered safe, the FBI said.

ISIS FLAG

An ISIS flag was attached to a staff protruding from the trailer hitch of the rented vehicle, prompting an investigation into possible links to terrorist organizations, the Federal Bureau of Investigation said.

U.S. President Joe Biden condemned what he called a "despicable" act and said investigators were looking into whether there might be a link to a Tesla truck fire outside a Trump hotel in Las Vegas. So far, there was no evidence linking the two events, the president and FBI said.

Public records showed Jabbar worked in real estate in Houston. In a promotional video posted four years ago, Jabbar described himself as born and raised in Beaumont, a city about 80 miles (130 km) east of Houston.

Jabbar was in the regular Army from March 2007 until January 2015 and then in the Army Reserve from January 2015 until July 2020, an Army spokesperson said. He deployed to Afghanistan from February 2009 to January 2010 and held the rank of staff sergeant at the end of service.

CNN, citing officials briefed on the investigation, said the suspect recorded videos in which he mentioned dreams about joining ISIS and once contemplated killing his family after a divorce.

ISIS - also called Islamic State or ISIL - is a Muslim militant group that once imposed a reign of terror over millions of people in Iraq and Syria until it collapsed following a sustained military campaign by a U.S.-led coalition.

Even as it has been weakened in the field, ISIS has continued to recruit sympathizers online, experts say.

"This is not just an act of terrorism, this is evil," Police Chief Anne Kirkpatrick said.

(Reporting by Reuters staff; Editing by Scott Malone)