There is an excellent post at Volokh Conspiracy.
Here’s the problem in a nutshell: So much at trial can turn on the testimony of a police officer. For a criminal defendant, life and liberty may depend on the ability to impeach the officer’s testimony. The federal constitution, as interpreted by Brady v. Maryland and its progeny, requires prosecutors to disclose to defendants any favorable, material evidence known to the prosecution team, including evidence relating to a witness’s credibility. Much impeachment evidence can be found in a police officer’s personnel file. But in many jurisdictions, a thicket of state laws, local policies, and bare-knuckle political pressure prevents access to the material in these personnel files, despite the federal constitutional requirement to disclose. In the name of protecting police privacy, criminal defendants are denied their due process rights to a fair trial.
Here’s what I ask for in my discovery requests.
Any and all adverse or negative information contained in the personnel files of any federal or state law enforcement agent who may have worked on this case in any manner. This includes, but is not limited to: Any “on-the-job” or field training records, training test score results, evidence of credentials having ever been suspended or revoked, and investigations regardless of result into allegations of malpractice. The defense does not agree that United States v. Henthorn sets the appropriate standard of production on this issue, in military cases. In fact some years ago I had a case where the NCIS gave a Henthorn disclosure to the prosecutor which turned out to be substantially and materially false.