Mayor Stephanie Rawlings-Blake offered a new explanation Wednesday for why her administration never acted on the results of an audit that found a high error rate for city speed camera tickets: The national engineering firm the city hired was "not sufficiently qualified" to do a thorough report.

She also said the 90-page audit by engineering consultant URS Corp. was "incomplete."

"It was clear from that document that the company was not sufficiently qualified to do a complete review," Rawlings-Blake told reporters at a news conference Wednesday at City Hall. The mayor fielded questions about the audit, which the administration received in April and has never released.

She did not address why the city hired URS this month to do another $237,000 worth of work — "additional independent monitoring services" of speed and red-light cameras, among other tasks, according to city documents. The mayor's spokesman, Kevin Harris, said the work is separate from the speed camera audit.

The audit was part of $278,000 in work that URS did for the city last year. Rawlings-Blake said Wednesday that she did not remember when she learned of the audit, but said she hadn't read the entire document until The Baltimore Sun posted it online last week after receiving a leaked copy.

URS evaluated the camera system as run by Xerox State and Local Solutions in 2012 and found an error rate of more than 10 percent — 40 times higher than city officials had acknowledged.

The mayor said the news media are beating a "dead horse" by continuing to report on errors with the city's speed camera program, which was shut down last year amid accuracy concerns.

"The goal is to protect our kids as they're going to and from school," she said. "I've heard people say they're no longer paying attention to their speed. They're speeding because they know the cameras are down. That's not helpful to our kids, who we want to make safe."

URS officials did not respond to a request for comment.

The City Council decided Monday to investigate the circumstances surrounding the audit and why the Rawlings-Blake administration never released it and other documents to the public.

"Everything is not being shared with us," said City Councilwoman Sharon Green Middleton. "We shouldn't have to try to pull information out of the administration. They should be willing to share everything with the council members so we can explain what's happening to our constituents."

Middleton said some of the problem cameras were located in her Northwest Baltimore district.

"That was very upsetting," she said. "There definitely needs to be an investigation because there's a lot of unanswered questions that the public needs to know. We want to keep government transparent. We want our citizens to trust us and trust the government."

For the audit, URS looked at a sample of nearly 1,000 tickets from a random day in 2012 at 37 of the city's 83 speed cameras. The firm said it could vouch for the accuracy of about only 64 percent of the tickets. More than 10 percent were found to be in error. Another 26 percent were described as questionable.

The document contained caveats. URS said it ran out of time to review citations from all of the city's cameras and therefore submitted findings for the 37 it did analyze. The company also said that camera vendor Xerox might be able to explain some of the problems.

During her comments Wednesday, Rawlings-Blake emphasized that the city has refunded erroneous tickets and shut down the entire speed camera system in April amid accuracy concerns.

"Every time that we saw an incident where a camera has an unacceptable error rate, the camera was taken down so it could be fixed, the incorrect citations were voided and refunds were given," she said.

However, officials have said that no refunds were issued as a result of the findings about the 37 cameras tested by URS. Thirteen cameras were found to have double-digit error rates.

Xerox was the city's speed camera vendor from the fall of 2009 through 2012. In response to a request from The Sun, Harris provided data showing that over the years, the city refunded 6,253 speed camera tickets issued by Xerox. The documents indicate that 3,091 tickets were refunded due to errors, while others were for different reasons, such as duplicate payments.

City Councilman Carl Stokes questioned why the administration was so critical of the independent review of Xerox's speed camera data.