The Brooklyn District Attorney will not prosecute a New York City subway rider who shot another man aboard a packed rush-hour train during an argument, according to a report.

"Yesterday's shooting inside a crowded subway car was shocking and deeply upsetting," spokesman Oren Yaniv said in a statement, NBC 4 New York reported. "The investigation into this tragic incident is ongoing but, at this stage, evidence of self-defense precludes us from filing any criminal charges against the shooter."

Police described the 36-year-old wounded man as the "aggressor" who pulled the gun in the altercation on the A train.

The 32-year-old man he was arguing with was able to grab the weapon and shoot the older man as the train approached the Hoyt-Schermerhorn stop around 4:45 p.m. as commuters in the packed train scrambled for cover.

Michael Kemper, the chief of transit for the NYPD, said that the alleged shooter was cooperating with detectives.

He said the incident appeared to begin when the 36-year-old confronted the other man and pulled the pistol, leading to a scuffle between the two men.

The older man was struck once in the head and was taken to New York-Presbyterian Brooklyn Methodist Hospital.

The shooting comes amid a series of high-profile crimes in the subway system, including a 29-year-old woman who lost both of her feet after she was shoved in front of an oncoming train at the Fulton Street station last Saturday.

That occurred just days after Gov. Kathy Hochul announed that she would be sending National Guard troops and State Police to patrol in the subway to protect commuters.

"These brazen heinous attacks on our subway system will not be tolerated," Hochul said at the announcement.

This is a developing story.