Updated at 5:30 a.m.

Police were trying to track down the renter of a van possibly connected to the violence in New York City’s subway Tuesday, when a gunman set off a smoke grenade and fired a barrage of bullets in a rush-hour subway train, shooting at least 10 people. 

Police Chief of Detectives James Essig said investigators weren’t sure whether the man, identified as Frank R. James, 62, had any link to the subway attack.

Authorities also were looking into social media posts by someone with the same name that mentioned homelessness, New York and Mayor Adams, leading officials to tighten the mayor’s security detail, Chief Essig and Police Commissioner Keechant Sewell said. She said the posts were “concerning.”

Authorities were examining social media videos in which Mr. James decried the United States as a racist place awash in violence and sometimes railed against Mr. Adams.

“This nation was born in violence, it’s kept alive by violence or the threat thereof and it’s going to die a violent death. There’s nothing going to stop that,” Mr. James said in one video.

Rambling, profanity-filled videos apparently posted on YouTube by Mr. James, who is Black, are replete with violent language and bigoted comments, some against other Black people.

One video, posted April 11, criticizes crime against Black people and says drastic action is needed.

“You got kids going in here now taking machine guns and mowing down innocent people,” Mr. James says. “It’s not going to get better until we make it better,” he said, adding that he thought things would only change if certain people were “stomped, kicked and tortured” out of their “comfort zone.”

Several videos mention New York’s subways.

A Feb. 20 video says the mayor and governor’s plan to address homelessness and safety in the subway system “is doomed for failure” and refers to himself as a “victim” of the city’s mental health programs. A Jan. 25 video criticizes Mr. Adams’ plan to end gun violence.

As police searched for the shooter, Governor Hochul warned New Yorkers to be vigilant.

“This individual is still on the loose. This person is dangerous,” she said at a news conference. 

Ms. Sewell said the attack was not being investigated as terrorism, but that she was “not ruling out anything.” The shooter’s motive was unknown.

Authorities found a 9 mm semi-automatic handgun at the scene, along with extended magazines, a hatchet, detonated and undetonated smoke grenades, a black garbage can, a rolling cart, gasoline and the key to a U-Haul van, Chief Essig said.

He said the key led investigators to the van renter, finding that he has addresses in Philadelphia and Wisconsin.

The officials said authorities zeroed in on a person of interest after the credit card used to rent the van was found at the shooting scene.

The van was found, unoccupied, elsewhere in Brooklyn.

Investigators believe the weapon jammed, preventing the suspect from continuing to fire, the officials said. The federal Bureau of Alcohol, Tobacco, Firearms and Explosives has completed an urgent trace to identify the gun’s manufacturer, seller and initial owner.

The morning rush hour attack made the subway a scene of horror: a smoke-filled car with at least 33 rounds of gunfire going off, police said. Frightened commuters ran from the train and others limped out of it. At least one rider collapsed on the platform.

The gunfire erupted on a train that pulled into a station in the Sunset Park neighborhood, about a 15-minute ride from Manhattan and predominantly home to Hispanic and Asian communities.

Five people were in critical condition but expected to survive. At least 29 in all were treated at hospitals for gunshot wounds, smoke inhalation and other conditions, according to hospitals.

The attack unnerved a city on guard about a rise in gun violence and the ever-present threat of terrorism. It left some New Yorkers jittery about riding the nation’s busiest subway system and prompted officials to increase policing at transportation hubs from Philadelphia to Connecticut.

The Metropolitan Transportation Authority announced last fall that it had put security cameras in all 472 subway stations citywide, saying they would put criminals on an “express track to justice.” But at the station where the train arrived, the cameras apparently weren’t working.

MTA system chief Janno Lieber told TV interviewers he didn’t know why the cameras malfunctioned. But he said police had “a lot of different options” from cameras elsewhere on the subway line to get a glimpse of the shooter.