A private detective accused of trying to set up a Costa Mesa city councilman with a phony DUI and electronically tailing the city’s mayor pleaded guilty Wednesday to felony charges of false imprisonment and conspiracy to file a false police report.

Christopher Joseph Lanzillo reversed his previous not guilty plea during a hearing at the Santa Ana courthouse, admitting to four felony counts tied to the false DUI report against City Councilman Jim Righeimer and the use of a GPS tracking device to tail Costa Mesa Mayor Stephen Mensinger.

Lanzillo, a former Riverside police officer, was one of two private investigators who prosecutors say were at the center of an effort funded by the Costa Mesa Police Association to dig up dirt on Mensinger and Righeimer. The second private investigator, former Riverside detective Scott Impola, is still awaiting trial.

On Aug. 22, 2012, prosecutors say the two investigators called 911 after following Righeimer home from a Costa Mesa bar. Officers responded, and briefly detained Righeimer as they conducted a field sobriety test, which the councilman passed. In a subsequent news conference, Righeimer provided a receipt showing he had been drinking Diet Coke at the bar.

“We must remember what this case is about,” Righeimer said after Lanzillo’s guilty plea. “This case revolves around the Costa Mesa Police Association hiring private investigators to get information to extort elected officials for the benefit of their member’s salary and pensions. This is pure political corruption. Mr. Lanzillo and Mr. Impola worked at a law firm that represented over 130 Police Officer Associations. They worked full-time getting dirt on elected officials that could be used later to extort these same elected officials when their contract came up for negotiation. “

Lanzillo’s attorney, Edward Robinson, declined to comment on his clients guilty plea. The Costa Mesa police union has previously denied knowing about any wrongdoing.

Senior Deputy District Attorney Robert Mestman confirmed that Lanzillo was not offered a plea deal, instead admitting to all the charges he was facing.

“I think it speaks to the strength of our case,” Mestman said.

Mensinger also indicated that he was pleased with Lanzillo’s decision to plead guilty.

“I think the message is clear, that unions and their candidate operatives who are involved in extortion and dirty tricks will see justice served cold,” Mensinger said. “I’m elated with the plea and my family can put this chapter of the ongoing union nightmare to rest.”

Leaders of the Costa Mesa Police Association have acknowledged hiring Lanzillo and Impalla’s employer, now-defunct law firm Lackie, Dammeier, McGill & Ethir, to look into Mensinger, Righeimer, Costa Mesa Councilman Gary Monahan and candidate Colin McCarthy for “candidate research.”

The union was in the midst of a heated dispute with Righeimer and Mensinger over their efforts to outsource city services. Both councilmen are outspoken critics of public unions and their sway with government agencies.

The Costa Mesa Police Association has vehemently denied knowing about any illegal actions on the part of the hired law firm or its investigators.

During a court hearing late last year, Costa Mesa Officer Jason Chamness, who was president of the Costa Mesa police union in 2012, testified that he and his fellow union officials believed that Righeimer, Mensinger and Monahan posed a threat by threatening to cut back public safety funding.

In the wake of the Costa Mesa case, numerous other cities in California have accused Lackie, Dammeier, McGill & Ethir of trying to bully them into backing police unions and granting pay raises.

Lanzillo is scheduled to return to court for sentencing on Jan. 13. He faces up to four years and four months in prison.

Contact the writer: semery@scng.com