McCann is also implementing training on DUI cases for prosecutors that will emphasize recognizing potential problems with the Breathalyzer devices.
Finally, Jamerson said, the District Attorney's Office will start doing its own calibration checks on Breathalyzers rather than depend solely on police certification.
The real bill will be some time in coming.
Besides the cost of reviewing thousands of DUI prosecutions and likely retrying some, the police and city could face civil lawsuits by people wrongly convicted - some of whom may have lost their driver's license, their job, or their freedom.
Though police officials have a list of about 400 people affected by the miscalibrated machines, Jamerson said Williams had decided a full review was needed.
Though defense lawyers specializing in DUI cases said only two of the Police Department's eight Breathalyzers had proved inaccurate, police said Wednesday that the total was four. Some court-system sources said that number was likely to increase.
Jamerson said the District Attorney's Office did not know how many cases would be involved in the review and could not predict how long it would take.
"That's a lot of cases," said Bradley Bridge, an assistant public defender, whose office is reviewing DUI cases it handled.
Contrary to statements by some lawyers Wednesday, Jamerson said the District Attorney's Office had not dismissed any DUI cases because of the erroneous Breathalyzers.
A month ago, she said, the office sent letters to 416 defense lawyers based on the list that the police Accident Investigation Division had compiled.
Since then, Jamerson said, no lawyer has requested a new trial or dismissal of charges.
Breathalyzers use a person's breath to gauge whether the blood-alcohol level is above the 0.08-percent threshold to be charged with driving under the influence.
To ensure accuracy, the device must be calibrated by a testing lab and checked by a police operator against a measured test sample.
Police are investigating how the erroneous machines came to be used, Police Commissioner Charles H. Ramsey said. Prosecutor Nichols told reporters Wednesday that the officer operating the units had kept using them after tests showed they were not calibrated.
Police officials said that the officer in charge of calibration had been moved out of the job and that the captain of the Accident Investigation Division transferred to a night command post.
Philadelphia is not the only city where DUI prosecutions have been tainted because of miscalibrated Breathalyzers.
In February 2010, a consultant hired by Washington's police confirmed that Breathalyzers had not been checked for accuracy; a programming error went undetected.
Since then, officials in that city have identified about 400 affected people convicted of drunken driving, half of whom served some jail time. About 50 people affected have asked to have their convictions reversed, and 22 civil lawsuits have been filed.
Williams has said his office will not object if those convicted in Philadelphia based on the compromised Breathalyzers ask for a new trial.
The number of DUI cases that may be dismissed is difficult to determine, legal experts said, because they are rarely based only on a Breathalyzer test.
Even without test results, a prosecutor may have the arresting officer testify about a driver's "general impairment" - symptoms such as unsteady gait, slurring of words, or the odor of alcohol on the breath.
Defense attorneys have challenged the accuracy of police technology, including Breathalyzers and radar guns, for years. Defense lawyers got new support for their challenges in the U.S. Supreme Court's 2009 Melendez-Diaz v. Massachusetts ruling, which held that analysts in forensic lab reports must be made available at trial for defense questioning.
Contact staff writer Joseph A. Slobodzian at 215-854-2985 or firstname.lastname@example.org.