Jan Goldsmith told NBC 7 that since January, when the Filner administration really got under way, the mayor began playing fast and loose with city money.
Now, Goldsmith said Filner's "brazen" character and conduct figure to cost him his office.
"It's not a matter of 'if', it is a matter of 'when,’ Goldsmith said. "At this point, we're going to give him an out. It's his choice. If he wants to resign, he's going to have some opportunity. I can't go into everything -- because I won't."
In response to a request about if the City Charter allows for any other avenue other than a recall effort to remove an elected mayor, Goldsmith issued a memo Thursday explaining a potential loophole.
According to Goldsmith, Section 108 states that "every City officer who willfully approves or allows unauthorized payments from the City treasury is subject to removal from office."
Filner is already under intense pressure to resign his position because of allegations of wide-ranging sexual harassment, with his most recent accuser a great-grandmother.
Goldsmith said Filner "intentionally, consciously" began leaving the city attorney's office in the dark regarding legal reviews of his spending of taxpayer dollars:
Amid the allegations of sexual harassment and unwanted sexual advances, there have been reports of questionable financial dealings tied to the mayor's office.
Checks from a developer to the City totaling $100,000 were returned by the mayor after a federal investigation was launched.
Mayor Filner said he would pay for a trip to Paris in June after the travel drew questions about whether state limits on gifts were violated.
City Councilmember Kevin Faulconer, the Audit Committee Chairman, has been questioning the $21,000 charged to city-issued credit cards for the trip. Faulconer has asked the City’s COO to release all credit card invoices associated with the Mayor’s trip by Aug. 28.
Also, NBC 7 Investigates has learned Mayor Bob Filner charged $511 at the Westgate Hotel on a city-issued credit card.
The credit card statements show eight charges over a five-month period between January and May to the luxury hotel across the street from City Hall.