A trail of clues in online rants, a rented van and a fireworks purchase.

The New York Police Division fanned throughout the 5 boroughs early Wednesday trying to find clues and provided a $50,000 reward for data that results in the arrest of the gunman who fired 33 pictures on a rush-hour subway practice in Brooklyn.

New York police officers and their federal counterparts requested particularly that folks share cellphone video from the taking pictures website or elsewhere that may assist convey the manhunt to a swift conclusion. Police have recognized an individual of curiosity and stated the reward may go to those that assist discover him.

“Everybody’s obtained a cellphone of their pocket,” Michael J. Driscoll, the assistant director in control of the F.B.I.’s New York workplace, stated at a Tuesday night information convention. “There’s quite a lot of video on the market.”

The preliminary topic of the search was Frank R. James, the 62-year-old man recognized as an individual of curiosity within the case, with investigators focusing their rapid consideration on addresses in Milwaukee and Philadelphia the place he had lately lived.

Mr. James’s ties to Philadelphia, the police stated, included his current rental there of a van that he drove to an space of Brooklyn close to the subway line the place the taking pictures occurred and deserted.

The police stated that they had discovered a key to the van amongst varied different objects — a Glock 9-millimeter handgun, three ammunition magazines, a hatchet, fireworks and a liquid believed to be gasoline — that they believed the gunman had left on the practice. The van was discovered on a Brooklyn road a number of hours after the taking pictures.

“We’re endeavoring to find him to find out his connection to the subway taking pictures, if any,” James Essig, New York Metropolis’s chief of detectives, stated of Mr. James whereas talking on the information convention.

“We’re asking for anybody’s assist with data,” he added, whereas asserting the reward.

The fireworks discovered on the subway — {a photograph} of which circulated on social media Tuesday — appeared to open one other investigative path resulting in Mr. James. In keeping with a fireworks vendor in Racine, Wis., a person named Frank James purchased a number of comparable manufacturers of consumer-grade fireworks there final June.

Along with bodily and video proof, investigators had been additionally delving into Mr. James’s exercise on-line, the place he posted dozens of movies lately, a lot of them offended diatribes peppered with bigotry.

In his name for the general public’s assist, Mr. Driscoll of the F.B.I. urged individuals to contact the company about any on-line materials they believed to be related.

“When you have digital data that you simply’d prefer to share with us in reference to this investigation, please go to fbi.gov,” he stated.