A private detective and former Riverside police officer accused of trying to help set up Costa Mesa city leaders in the midst of a police union dispute has died while awaiting trial.

Scott Impola – one of two investigators accused of making a false DUI report against Councilman Jim Righeimer and using a GPS tracking device to tail then-Mayor Stephen Mensinger – died on July 10, the Orange County District Attorney’s Office announced on Friday. He was 49.

Impola’s attorney, David Vaughn, confirmed his client died of natural causes. He declined to comment further.

Along with former Riverside police Officer Christopher Lanzillo, Impola was accused of trying to dig up dirt on Mensinger and Righeimer, who at the time were in a heated dispute with union leaders in Costa Mesa over their efforts to outsource city services.

According to prosecutors, Lanzillo placed an electronic tracking device on Mensinger’s car when it was parked in his driveway. Lanzillo and Impola used the device to track Mensinger from July to August 2012, prosecutors alleged.

On Aug. 22, 2012, prosecutors say, the two investigators called 911 after following Righeimer home from a Costa Mesa bar, saying the councilman stumbled to his car and swerved while driving.

Officers responded and briefly detained Righeimer until a field-sobriety test confirmed that he was not inebriated. In a subsequent news conference, Righeimer provided a receipt from the bar that showed he had been drinking Diet Coke that night.

Lanzillo pleaded guilty to four felony conspiracy and false-imprisonment charges. In March, Lanzillo was sentenced to a year in jail.

During Lanzillo’s sentencing, Deputy District Attorney Chris Duff accused Lanzillo and Impola of bringing “dirty politics” to the county. The prosecutor said that the investigators broke the public’s trust by using the training they learned as police officers to go after the elected officials.

Impola and Lanzilla were working for the now-defunct Upland-based law firm Lackie, Dammeier, McGill & Ethir. The firm, which at one time represented more than 130 police unions throughout California, was paying the investigators to conduct research on Righeimer, Mensinger, former Councilman Gary Monahan and candidate Colin McCarthy.

Numerous cities have since accused the firm of trying to bully them into backing unions and their requests for pay raises. The Costa Mesa police union fired the law firm after the allegations against Lanzillo and Impola surfaced, and has denied knowing about any wrongdoing.

A jury trial for Impola had not yet been scheduled. On Wednesday, the DA’s office filed a motion to dismiss the charges against him, a request a judge is scheduled to take up at a Sept. 21 hearing.