A Chicago Police sergeant avoided a one-year suspension Thursday over the bungled homicide investigation that cleared then-Mayor Richard M. Daley’s nephew in the death of David Koschman.

The Chicago Police Board found Sgt. Sam Cirone guilty on all five counts of violating department rules in the investigation, but decided he should only receive a reprimand, allowing him to continue working.

“While the Board has found that Sergeant Cirone supervised an investigation that was not entirely thorough and the detectives under his supervision completed and submitted a [report] that was not entirely accurate and complete, the Board finds that responsibility for the failures in this investigation lie more in the hands of Deputy Chief of Detectives Constantine `Dean’ Andrews, who played a major role in designing an inaccurate [report],” according to the police board’s 30-page ruling.

“Sergeant Cirone failed as a supervisor, but his role in this investigation and his responsibility for its failures is clearly less than that of the actual detectives and those above him.”

Cirone had no comment Thursday as he left the police board meeting.

Andrews, who retired four years ago and avoided punishment in the case, and Cirone exchanged emails the night before the final report was submitted and approved in March 2011, concluding Daley’s nephew Richard “R.J.” Vanecko acted in self-defense when he punched Koschman during a drunken argument on Division Street in April 2011.

That final report stated that Koschman had yelled, “F- - - you, I’ll kick your ass,’’ but investigators for special prosecutor Dan K. Webb and city Inspector General Joseph Ferguson concluded there was no evidence that Koschman ever said those words.

Cirone, who followed in his father’s footsteps when he joined the police department 27 years ago, was the last of six officers who faced disciplinary action for closing the Koschman case without seeking criminal charges against Daley’s nephew.

Koschman’s death had been on the books for years as an unsolved homicide, until a Chicago Sun-Times reporter’s public records request in January 2011 to review the case reports spurred the police department to order a new investigation less than five months before Daley retired as mayor.

Cirone supervised detectives James Gilger and Nick Spanos, who spent two months on that reinvestigation. Their report agreed with the original findings that Daley’s nephew acted in self-defense when he threw the punch that caused Koschman’s death. And the police closed the case without any charges.

But a Sun-Times investigation cast doubt on the police findings. It documented the police department’s missteps in the 2004 and 2011 investigations, including failing to canvas the Division Street area for witnesses or videos of the drunken confrontation on Division Street near Dearborn in April 2004 during which Vanecko punched the significantly smaller Koschman.

Based on the Sun-Times’ reports, a Cook County judge appointed Webb as a special prosecutor. That led to Daley’s nephew being charged with involuntary manslaughter.

In 2014, Vanecko, now 45, pleaded guilty. He served 60 days in jail.

READ THE POLICE BOARD’S FULL RULING HERE:

Webb was critical of the police handling of the case but said he didn’t have enough evidence to charge any of the officers involved.

But his report led to an investigation by Ferguson, the city’s inspector general. In late 2015, Ferguson urged John Escalante, then the interim police superintendent, to fire Gilger, Spanos and Lt. Denis P. Walsh. The inspector general also recommended considering disciplinary action as severe as termination for Cirone, Andrews and Commander Joseph Salemme.

Escalante took steps to fire Walsh and Gilger and to issue one-year suspensions for the others.

But Walsh, Gilger, Andrews and Salemme retired, putting them beyond the range of any internal discipline.

Spanos got his one-year suspension cut to two months by cashing in accrued time off.

Cirone, with the backing of the police sergeants union, fought his one-year suspension all the way to the Illinois Supreme Court, which refused to hear his case.

Cirone has continued to make a six-figure salary during that time while also collecting tens of thousands of dollars in overtime pay and building his police pension. He now supervises five detectives who work on cold cases on the North Side and Northwest Side.

During a hearing before the police board in August, Cirone and some of the other cops involved in the case testified that he shouldn’t be punished because, despite the later guilty plea, there wasn’t any reason to charge Vanecko with killing Koschman.

Cirone’s lawyer James McKay blamed Koschman for his own death.

“I say this with all due respect to Mrs. [Nanci] Koschman,” McKay told the hearing officer, “the reason her son isn’t here today is because he started something he couldn’t finish.”

Two police board members — attorneys Steve Flores and Matthew Crowl — recused themselves from the Cirone decision. Flores and Webb are attorneys at Winston & Strawn. As Daley’s deputy mayor for public safety, Crowl informed the mayor about the Koschman case soon after it happened, but Webb’s report said, “It was not clear whether Mayor Daley was already aware of the incident when Crowl made the disclosure to him.”