In 2009, the U.S. Court of Appeals upheld long-established due process principles requiring prosecutors to disclose to the defense any information in the government's possession beneficial to the defendant, including any evidence which may impeach a government witness. 

At issue was the failure of the prosecutor to disclose the criminal history of a witness and the impact such information may have had on the defense's ability to call into question the witness's propensity for truthfulness and honesty.  

While it was unclear as to whether the prosecutor was actually in possession of the information, the Court found his investigators definitely were; thus, the prosecutor could not claim ignorance in order to escape his duty under Brady .

The ruling has led to two Southern California counties having to belatedly send out notices disclosing similar such evidence with regard to a particular criminalist in their employ.  Such impeachment evidence could easily compromise the government's ability to successfully prosecute any cases handled in the crime lab by that criminalist, be they cases involving DUIs, drugs, weapons or murder.