Orange County district attorney's office investigators showed up at Skosh Monahan's on Thursday to investigate the 911 call made last week about Costa Mesa Mayor Pro Tem Jim Righeimer.

Councilman Gary Monahan, owner of the bar and restaurant on Newport Boulevard, confirmed the meeting.

The D.A. subpoenaed the security video from Aug. 22, which was the night of the incident, Monahan said.

Costa Mesa police referred any inquiries to the district attorney's office. A spokeswoman for the district attorney, Farrah Emami, declined to comment.

A white SUV without license plates followed Righeimer from the restaurant to his home in Mesa Verde. Images of both vehicles can be seen leaving Skosh's on the tape, which the Daily Pilot has partially reviewed.

The 911 caller reported to police that Righeimer stumbled out of the bar and was speeding and swerving on the road. The video shows a few frames of Righeimer leaving without stumbling.

The caller, who identified himself as private investigator Chris Lanzillo, also reported to police that he thought Righeimer was driving under the influence of alcohol.

Righeimer, who said he only had a Diet Coke, was given a field sobriety test and found to be sober by a Costa Mesa police officer.

He termed the call a "setup" by his political opponents in public employee associations and said his driving that night was fine.

Lanzillo said in a statement that he did not set up Righeimer and questioned the validity of the quick sobriety check Righeimer was given because it did not involve a Breathalyzer test.

He could not be reached for comment Thursday night.

In two press conferences, Righeimer has argued that Lanzillo following him is evidence of public employee unions trying to stifle his political agenda. Representatives from organized labor have strongly denied any involvement in the incident.

Lanzillo, 42, is a former Riverside police detective and works as a private investigator for Lackie, Dammeier & McGill, a law firm that represents police unions throughout Southern California. The law firm represented the Costa Mesa Police Assn. (CMPA) at the time of the incident, but said it had nothing to do with the call.

The law firm denies Lanzillo was working for them at the time of the call, and Lanzillo has since said he was on a separate investigation when he decided to follow Righeimer and call police. When Lanzillo made the call, he told the 911 dispatcher he was meeting a friend in the area.

The CMPA has since broken off ties with Lackie, Dammeier & McGill, saying it wanted to take a more cooperative approach to negotiations with city officials. The law firm defended its strategy in a statement to the Pilot earlier this week.

joseph.serna@latimes.com

Twitter: @JosephSerna