The probe involves several accounts at the Greater Pittsburgh Police Federal Credit Union, from which the FBI seized documents on Thursday.
"We want to do a thorough analysis and find out where the money was spent, was it appropriately spent, who used it, who had debit cards, and really get all those questions answered," Ravenstahl said.
The mayor said he doesn't know why money from one account paid to rent condos downtown for officials whose homes were threatened by Group of 20 economic summit protesters in 2009. State and federal money reimbursed the city for its G20-related expenses, including the condos, he said.
Ravenstahl's remarks come one week after federal agents gathered boxes of records from police headquarters and a few days after City Controller Michael Lamb announced an audit of the force's Special Events office.
Lamb said he wants to see how police handle payments they receive for off-duty officers hired to work private security details. The credit union is not an authorized depository for city money, he noted.
Ravenstahl said it's not yet clear if any funds have been improperly deposited or spent.
The mayor had already called for a review of the police bureau on Feb. 8 after learning that Chief Nate Harper partnered with four subordinates to form a private security firm. Former Washington County District Attorney Steven M. Toprani has been tapped to lead that effort.
Harper has denied wrongdoing.