An off-duty firefighter gives CPR to Joshua Beal after off-duty Chicago police officer Joseph Treacy (in red T-shirt) and an off-duty sergeant (in a black Sox sweatshirt over a white uniform shirt) — fired at Beal on 111th near Kedzie on Nov. 5, 2016. | Civilian Office of Police Accountability video

The Chicago Police Department suspended an officer for three months for failing to register a handgun he used to open fire at a man killed in a racially charged disturbance in 2016 on the Southwest Side.

The gun was one of eight firearms Officer Joseph Treacy owned but didn’t register with the department, officials say.

The Chicago Sun-Times has reported that authorities were looking at Treacy’s gun ownership, but the outcome of that scrutiny has previously been unknown.

Former Chicago Police Supt. Eddie Johnson originally disagreed with the Civilian Office of Police Accountability’s recommendation to suspend Treacy for 90 days for failing to register his gun.

Johnson thought a three-day suspension was in line with similar cases, a police spokesman said. But Johnson eventually agreed last year to suspend Treacy for three months. Treacy appealed the suspension.

Officials could not immediately provide the date of the suspension.

The Civilian Office of Police Accountability had referred the issue of Treacy’s other seven unregistered guns to the police department’s Bureau of Internal Affairs for investigation, said Ephraim Eaddy, a spokesman for COPA.

In a separate investigation, COPA found Treacy and a sergeant — who were both off-duty — were justified when they used deadly force against Joshua Beal in 2016. The Indiana man pointed a gun at them during a confrontation in the Southwest Side Mount Greenwood neighborhood, police said.

Beal’s shooting appears to have been linked to a traffic altercation between Treacy, who’s white, and African-Americans, including Beal, who were driving in a funeral procession. They jumped out of their cars on 111th Street near Kedzie, a crowd gathered and racial slurs were used, according to a report by COPA.

A cellphone video shows Beal standing behind a car with a gun in his hand. The off-duty officers shot at Beal after he extended his arm to fire at them, police said.

Beal’s family has filed a lawsuit against the city over his death.