A day after filing criminal charges against a former aide to Mayor Kevin Johnson, the Sacramento County District Attorney's Office said Wednesday it will not charge a second former aide caught up in an investigation of city credit card use.

Credit card charges by Keith Hart, who was the chief service officer in the mayor's office, drew the attention of police investigators earlier this year when they were examining the credit charges of Lisa Serna-Mayorga, who was arrested Tuesday.

The police forwarded the results of their investigation to the District Attorney's Office, which made the decision Tuesday not to file charges against Hart, Assistant District Attorney Albert Locher said.

That would appear to leave Serna-Mayorga as the only criminal target of the probe. According to city Auditor Jorge Oseguera, police reviewed five years of credit card charges by city employees, and Serna-Mayorga and Hart were the only ones to have made charges that were potentially criminal.

Hart made three charges that raised questions. Each instance "appeared to be an accidental or mistaken use of the city card for a personal expense," according to a case disposition notice signed by Michael Blazina, supervising deputy district attorney. "For each (charge), immediately upon realizing he had made an inappropriate purchase, Hart acknowledged his conduct and timely reimbursed the city for the amount."

The charges in question were $80 to Geico Insurance, $142 to the Grand Ballroom on J Street and $92 for a tuxedo rental from Men's Wearhouse.

Hart told investigators he mistakenly used his city credit card for the insurance and ballroom charges because it looked like one of his personal cards, according to the disposition notice.

He knowingly rented the tuxedo with the city card because he needed it for an event representing the mayor, according to the notice. But he paid the city back when he was told it wasn't appropriate to charge the city.

The indictment against Serna-Mayorga alleges that from July 2009 to June 2012, she used a city credit card for personal items totaling more than $19,000, including trips to Disneyland, hotel charges in Bodega Bay and Monterey, makeup, grocery bills and numerous iTunes items.

She was freed from jail late Tuesday and is scheduled for arraignment in Sacramento Superior Court on Dec. 26.

Serna-Mayorga is the daughter of the late Sacramento Mayor Joe Serna Jr. and the sister of Sacramento County Supervisor Phil Serna.

She is being represented by Linda Parisi, one of the region's highest-profile criminal defense attorneys. Parisi did not return messages Wednesday seeking comment on the charges against Serna-Mayorga.

Oseguera, the city auditor, said attention on Serna-Mayorga's case has likely had at least one benefit.

"One thing that's guaranteed is that this level of exposure provides some insurance that people won't do this sort of thing in the future," he said.

Oseguera completed an audit of city credit card use earlier this year and made a number of recommendations, including improving the process for approval of charges.

He said the city appears to have followed through on his recommendation for approvals but he won't be sure until he completes a report next month.

Oseguera said the city manager's office also has cut back the number of city-issued cards from 300 to somewhere in the low 200s following his finding that too many employees had cards.

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