The former aide to Sacramento Mayor Kevin Johnson who allegedly used her city-issued credit card for personal purchases is now the subject of a criminal investigation.

Sacramento police officials announced Wednesday they were investigating the credit card use of Lisa Serna-Mayorga, who sources said resigned last week after it was revealed she had bought $9,000 in personal items on her city card. Those purchases included a trip to Disneyland, gasoline and groceries, the sources said.

"Like anything else, when someone is entitled with the public trust and there's an accusation of misconduct, we need to investigate it thoroughly," Police Chief Rick Braziel said.

Serna-Mayorga signed a "Purchasing Card Request" in December 2008, soon after she was appointed by Johnson to serve as the City Council operations manager. In signing that form, a copy of which was obtained by The Bee, Serna-Mayorga agreed "that use of the Purchasing Card for any purpose other than City business is a crime, and will be prosecuted," according to the document.

That statement has become the basis for the criminal probe, officials said.

"It warrants this because of the circumstances and the evidence we've seen so far, that things that were non-business related were charged to a city credit card and only much later were there attempts to repay that," City Manager John Shirey said.

Serna-Mayorga could not be reached for comment on Wednesday.

She did not return an email seeking comment and the voice mailbox at her home is full.

Joaquin McPeek, a spokesman for Johnson, said, "the mayor is fully supportive of the investigation."

"While he remains saddened and disappointed by the conduct in question, he will always insist on full accountability for all city employees entrusted with public dollars," McPeek said.

Councilman Darrell Fong, a former police captain, said he thinks the criminal investigation "is warranted."

"There probably is enough there to conduct an investigation," he said.

The probe could take weeks. City staff members are still gathering Serna-Mayorga's credit card statements, many of which are available in hard copy only.

While Shirey said Tuesday that the mayor's chief of staff was responsible for authorizing Serna-Mayorga's credit card use on a monthly basis, the probe likely won't involve members of the mayor's office, Braziel said. His rationale: Serna-Mayorga was not technically a member of Johnson's staff when the charges in question occurred, even though he appointed her to the council operations post.

According to sources, a fiscal year review of Serna-Mayorga's credit card expenses in June revealed she had used the card to make $3,000 in personal charges over the past year. Serna-Mayorga reimbursed the city that $3,000.

The review of Serna-Mayorga's expenses took place as she was transitioning from the council operations post to a job in the mayor's office as director of constituent affairs. As council operations manager, Serna-Mayorga oversaw the expenses and other daily tasks for the mayor and City Council offices.

Further digging found another $6,000 in personal charges in previous years, the sources said. Serna-Mayorga reimbursed the city another $6,000 before resigning July 19, according to the sources.

Serna-Mayorga is the daughter of former Mayor Joe Serna Jr., who died in 1999. Her brother, Phil Serna, is a Sacramento County supervisor.

She has been a close supporter of the mayor's for many years.

She has been active in the leadership of the St. HOPE Public Schools – the nonprofit founded by Johnson that operates charter schools in Oak Park – and was among Johnson's first hires after he was elected mayor in 2008.

The scandal has led to broader concerns over the use of credit cards at City Hall.

Councilman Steve Cohn, chairman of the council's audit committee, said Wednesday he wants to push up a planned audit of citywide credit card use.

City Auditor Jorge Oseguera had not planned to launch that audit until September due to limited staffing; the auditor assigned to the credit card work is finishing up another audit. But Cohn said he wants the examination finished by September.

"I think given the high profile of this incident that occurred in the mayor's office, it would behoove us to get the results of that audit back as soon as possible," Cohn said.

Cohn also will ask that Shirey hire an outside auditor to look at the credit card use of the mayor and City Council offices.

Oseguera reports directly to the council and mayor, and the auditor said he could not examine his bosses' credit cards because it would be a conflict of interest.

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