The FBI is investigating social media posts and videos investigators believe are linked to Frank James, the suspect being sought in Tuesday’s shooting in a Brooklyn subway, Fox News Digital has learned.

A senior law enforcement source told Fox News on Wednesday that some of James' posts were critical of New York City Mayor Eric Adams. Fox News Digital viewed a string of rambling, profanity-laced YouTube videos in which a man who is apparently James decries the United States as a racist, violent place.

BROOKLYN SUBWAY SHOOTING: LIVE UPDATES

"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," James said in one video.

NYPD have identified Frank James as a person of interest in the Brooklyn subway shooting.  (NYPD)

Despite some reporting from other sources, the law enforcement source said the FBI did not open a prior file on James out of New Mexico.

James remains on the loose and authorities are trying to track him down based on his prior contacts in Philadelphia and Wisconsin, according to the source.

On Wednesday morning, Adams confirmed to Fox News that James was now the lone suspect in the attack.

The shooting in the crowded 36th Street subway station in the Sunset Park neighborhood happened around 8:25 a.m. as the Manhattan-bound N train pulled into the station, police said. 

A man in a bright nylon safety vest and gas mask opened a smoke canister and fired off at least 33 rounds from a 9 mm Glock handgun. The attack left 10 people shot.

New York City Police Department personnel gather at the entrance to a subway stop in the Brooklyn borough of New York, Tuesday, April 12, 2022. (AP Photo/John Minchillo)

New York City Police Department personnel gather at the entrance to a subway stop in Brooklyn, New York, Tuesday, April 12, 2022. (AP Photo/John Minchillo)

Police said five of the gunshot victims were in critical condition but all 10 wounded in the shooting were expected to survive. At least a dozen others who escaped gunshot wounds were treated for smoke inhalation and other injuries.

The shooter fled in the chaos, leaving behind the gun, 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.

Brooklyn subway shooting

Passengers run from a subway car in a station in Brooklyn, New York, Tuesday, April 12, 2022. (Will B. Wylde via AP)

The van key led investigators to James, NYPD Chief of Detectives James Essig said, adding that the van was later found, unoccupied, near a station where investigators determined the gunman had entered the subway system.

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Police announced a $50,000 reward for information in the case.

Anyone with information is asked to call New York City Crime Stoppers at 1-800-577-TIPS.

The Associated Press contributed to this report.