The FBI is assisting the Cook County state’s attorney’s office as it considers “possible criminal charges” after a Chicago police officer shot a man inside a busy CTA Red Line station Friday evening, officials said a day after the controversial video-recorded encounter.

The shooting at the Grand station sparked outrage as cellphone video circulated on social media, with Mayor Lori Lightfoot calling it “extremely disturbing” and civil liberties advocates decrying the use of force.

“The Chicago Police Department contacted the Cook County State’s Attorney’s Office to review the officer-involved shooting that occurred at a CTA Red Line station on February 28, 2020 for possible criminal charges,” State’s Attorney Kim Foxx’s office said in a statement. “We are working in partnership with the FBI on this investigation and will be unable to comment further while it is pending.”

Police officials, too, said they have “significant questions” about the shooting that happened about 4:15 p.m. after officers saw the man walking between train cars and tried to stop him.

A pair of videos show two officers struggling with the man for several minutes, deploying a stun gun and pepper spray as dozens of commuters mill about nearby.

One of the officers yells, “Shoot him!” and the other does. The man runs up the escalator, and a second shot can be heard off-screen.

He was taken to a hospital in critical condition but is expected to survive, officials said.

The American Civil Liberties Union of Illinois on Saturday slammed “the lack of meaningful de-escalation by Chicago police officers” as seen on video, and called for a full investigation.

“A man who apparently did nothing more than jumped trains ultimately was shot yesterday by a police officer, an event captured on video by a fellow CTA rider,” ACLU Illinois staff attorney Rachel Murphy said in a statement.

“The consent decree guiding police reform approved a year ago requires officers to use de-escalation techniques to prevent or reduce the need for force,” Murphy said. “It is critical that the community be part of the dialogue around when and how officers may use force.”

The shooting happened just hours after Lightfoot and interim Police Supt. Charlie Beck announced plans to add more police officers to the transit system, following a spate of violence on CTA trains and platforms in recent weeks.

“With the strong caveat that one perspective does not depict the entirety of the incident, the video is extremely disturbing and the actions by these officers are deeply concerning,” Lightfoot said in a tweet Friday night.