Officials in the Bronx and Brooklyn district attorneys’ offices say they are on Mr. Vance’s side in the debate, but they have less leverage over the Police Department than Manhattan does. One reason the Manhattan office has clout is that four years ago the police agreed to provide electronic, searchable copies of investigative reports to Mr. Vance’s office in return for $20 million to upgrade fiber-optic capacity.

So far police officials have rejected Mr. Vance’s requests.

For decades, the Police Department has turned over disciplinary records of officers only when a prosecutor asks for a background check on an officer who is going to testify at a hearing or trial, said Lawrence Byrne, the deputy police commissioner for legal affairs. The process has been streamlined in recent years, with one person designated to field requests from prosecutors and additional staff assigned to digging up the records, he said.

Still, the state’s highest court has upheld the principle that prosecutors do not need to delve into an officer’s personnel record to determine if enough evidence exists to warrant an arrest, Mr. Byrne argued. That scrutiny of an officer’s history can wait until trial, the court said.

“Whether an officer was disciplined five years ago for making a bad stop has nothing to do with whether a defendant today murdered his mother,” Mr. Byrne said. “It may bear on whether people will believe that officer at trial, but it doesn’t bear on the issue of whether the defendant murdered his mother.”

But nine out of 10 cases never get to a hearing or trial, prosecutors note. Instead, the defendant, who is often jailed, pleads guilty to the charge before the prosecutor or the defense ever learn if the officers involved have a checkered history.

The same is true of investigative reports. Defense attorneys say their clients often make decisions on a plea with only a sketchy knowledge of the witnesses against them.