Williams said he expected a good portion of the convictions to hold up without the results, based on other evidence. But he also acknowledged that some people might have been wrongly convicted of driving under the influence due to the mistake, and said his office was reaching out to people who faced charges during that period.
"Our interest is justice, not just convictions," he said.
Four of the Police Department's eight Breathalyzer machines gave false readings for tests administered to gauge whether a driver's blood-alcohol content is above the legal limit of 0.08 percent.
The problem was brought to the attention of the District Attorney's Office last month by Joseph Kelly, an 11-year lawyer in Port Richmond who has specialized in DUI cases and noticed the error in a calibration report.
"This has an impact on a lot of people, working people who need to have a driver's license to earn a living," said Kelly, who said much of his work came through the labor unions.
Police initially believed about 400 cases were affected but learned this week that the figure was almost triple that. Officials said more cases could come under scrutiny.
Ramsey said the officer in charge of calibrating the machines had been moved out of the job. Ramsey did not identify the officer but said an investigation was continuing into how and why the mistake had happened.
Police officials later said Capt. Michael Murphy, head of the department's Accident Investigation Division, had been transferred to a night command post in light of the disclosures.
A court source close to the investigation called the developments "an embarrassment" to the Police Department, which has faced scrutiny in recent years over corruption scandals and arrests of officers.
