A Texas man who expressed support for the Islamic State before he drove into a crowd in New Orleans on New Year’s Day, killing 14 people, appears to have acted alone, an F.B.I. official said on Thursday, as the city reopened Bourbon Street after the attack and hosted thousands of fans for the Sugar Bowl.

Investigators have found “no definitive link” between the attack and the explosion of a Tesla Cybertruck hours later that wounded at least seven people outside of a Trump hotel in Las Vegas, according to the F.B.I. official, Christopher Raia, the deputy assistant director of the bureau’s counterterrorism division.

The driver of the Cybertruck was identified on Thursday as an Army master sergeant from Colorado who had been on leave from active duty and had shot himself in the head just before the explosion. Mr. Raia cautioned that investigators were early in their inquiry and had not ruled anything out.

Mr. Raia said that based on hundreds of interviews and reviews of phone calls, social media accounts and electronic devices linked to the Texas man who carried out the attack in New Orleans, investigators no longer believed, as they said on Wednesday, that he had co-conspirators.

“We’re confident, at this point, that there are no accomplices,” Mr. Raia said at a news conference in New Orleans. Investigators have identified the man, who was killed in a shootout with the police, as Shamsud-Din Bahar Jabbar, 42, an American citizen from Texas.