A gunman walked up to a car in Chicago’s posh River North neighborhood and without saying a word opened fire killing an off-duty police officer who was leaving a nightclub with three friends, authorities said.

Chicago Police Department Officer John P. Rivera, 23, was sitting in the driver’s seat about 3 a.m. when at least one gunman, and possibly two-to-three other people, approached the car.

One man started “indiscriminately” firing into the car, unloading six-to-eight rounds, and striking Rivera in the torso, according to Anthony Guglielmi, the chief spokesman for the Chicago Police Department.

The suspected shooter remains at large. The department did question a person of interest related to the shooting, but authorities do not believe he is the actual shooter, Guglielmi said.

Another passenger who was shot underwent surgery and is listed in critical condition, Guglielmi said.

The two other passengers, a male Chicago police department member and woman, were also in the vehicle. They were not injured during the shooting.

It’s unclear what prompted the shooting, Guglielmi said.

While the area is “heavily saturated” with crime cameras, the department does not yet have video documenting an encounter between the Rivera’s group and the suspected shooter’s group.

“We have video documenting the [shooting] itself, but nothing earlier,” Guglielmi said, later explaining, “We’re actively canvassing for additional private video.”

At present, there is no evidence indicating that the shooter knew Rivera, nor is there evidence that the officer was targeted, Guglielmi said.

Rivera had handled a murder case on his shift Thursday night, but police are not speculating whether that investigation is connected to this crime, according to local press reports.

A motorcade of police vehicles with blue lights flashing escorted the fallen officer to the coroner’s office where an autopsy will be conducted Sunday.

Police are surveying local CCTV cameras from local businesses but so far do not see that there was a confrontation between the off-duty cop and his assailant. “There’s no problems, there’s no words exchanged,” Deputy Police Supt. Anthony Riccio told reporters at the scene Saturday morning.

“It’s a very sad day, we’re mourning the loss of another Chicago police officer,” Fraternal Order of Police President Kevin Graham said in a statement.

The shooting happened a few blocks from the Sound Bar, where a security officer was killed earlier this month.