NEW YORK (AP) — A gunman in a gas mask and construction vest set off smoke grenades and fired a barrage of bullets in a rush-hour subway train in Brooklyn, wounding at least 10 people Tuesday, authorities said. Police were trying to track down the renter of a van possibly connected to the violence.

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 were looking at his apparent social media posts, some of which led officials to tighten New York Mayor Eric Adams’ security detail. Police Commissioner Keechant Sewell called the posts “concerning.”

The attack turned the morning commute into a scene of horror: a smoke-filled underground car, an onslaught of at least 33 bullets, screaming riders running through a station, bloodied people lying on the platform as others tended to them.

In the train, Jordan Javier thought the first popping sound he heard was a textbook dropping. Then there was another pop, people started moving toward the front of the car, and he realized there was smoke, he said.

(Story continues below the video.)

When the train pulled into the station, people ran out and were directed to another train across the platform. Passengers wept and prayed as they rode, Javier said.

“I’m just grateful to be alive,” he said.

Five gunshot victims were in critical condition but expected to survive. At least a dozen people who escaped gunshot wounds were treated for smoke inhalation and other injuries.

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

Police are looking for Frank James as a person of interest in connection with a shooting on a Brooklyn subway on April 12, 2022. (Credit: NYPD)

Sitting in the back of the train’s second car, the gunman tossed two smoke grenades on the floor, pulled out a Glock 9 mm semi-automatic handgun and started firing, Essig said. He said police later found the weapon, 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.

That key led investigators to James, who has addresses in Philadelphia and Wisconsin, the detective chief said. The van was later found, unoccupied, near a subway station where investigators determined the gunman had entered the train system, Essig said.

Rambling, profanity-filled YouTube videos apparently posted by James, who is Black, are replete with Black nationalist rhetoric, violent language and bigoted comments, some of them directed at other Black people.

One, posted April 11, rails against crime against Black people and says drastic action is needed to change things. Another, from March 20, says the nation was “born in violence, it’s kept alive by violence or the threat thereof and it’s going to die a violent death.”

A Feb. 20 video says the mayor and governor’s plan to improve safety in New York City’s subway system “is doomed for failure” and refers to himself as a “victim” of the mayor’s mental health program. A Jan. 25 video — called “Dear Mr. Mayor” — is somewhat critical of Adams’ plan to end gun violence.

Investigators believe the shooter’s gun jammed, preventing the suspect from continuing to fire, said two law enforcement officials who weren’t authorized to discuss the investigation and spoke on condition of anonymity.

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.

(Story continues below the video.)

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 cameras weren’t working at three stations where police went to look for evidence Tuesday, Essig said.

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 lenses elsewhere on the subway line.

Riders’ videos show a person in a hooded sweatshirt raising an arm and pointing at something as five bangs sound, and smoke and people pouring out of a subway car, some limping and at least one collapsing on the platform. Other video and photos from the scene show people lying on the bloodied platform and the floor of a subway car.

Rider Juliana Fonda, a broadcast engineer at WNYC-FM, told its news site Gothamist that passengers from the car behind hers started banging on the connecting door.

“There was a lot of loud pops, and there was smoke in the other car,” she said. “And people were trying to get in and they couldn’t, they were pounding on the door to get into our car.”

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

“This individual is still on the loose. This person is dangerous,” the Democrat said at a news conference just after noon.

(Story continues below the video.)

After people streamed out of the train, quick-thinking transit workers ushered passengers to another train across the platform for safety, transit officials said.

High school student John Butsikaris was riding the other train and initially thought the problem might be mundane until the next stop, when he heard screams for medical attention and his train was evacuated.

“I’m definitely shook,” the 15-year-old told The Associated Press. “Even though I didn’t see what happened, I’m still scared, because it was like a few feet away from me, what happened.”

In Menlo, Iowa, President Joe Biden praised “the first responders who jumped in action, including civilians, civilians, who didn’t hesitate to help their fellow passengers and tried to shield them.”

Adams, who is isolating following a positive COVID-19 test on Sunday, said in a video statement that the city “will not allow New Yorkers to be terrorized, even by a single individual.”

New York City has faced a spate of shootings and high-profile bloodshed in recent months, including on the city’s subways. One of the most shocking was in January, when a woman was pushed to her death in front of a train by a stranger.

Adams, a Democrat a little over 100 days into his term, has made cracking down on crime — especially on the subways — a focus of his early administration, pledging to send more police officers into stations and platforms for regular patrols. It wasn’t immediately clear whether officers were already inside the station when the shootings occurred.

“It is going to take the entire nation to speak out and push back against the cult of death that has taken hold in this nation,” Adams said by video Tuesday night.