Federal prosecutors in Maryland are warning about the possibility of “seriously disrupted” criminal investigations following a U.S. appeals court ruling that questioned the integrity of allowing government agents to use their own internal teams, and not the courts, to review certain materials seized during the execution of search warrants.

The U.S. Court of Appeals for the Fourth Circuit assailed Maryland prosecutors last year for using a so-called filter team to review documents and email files taken from the offices of a Baltimore law firm as part of an ongoing criminal investigation. The appeals panel said a federal magistrate judge, and not investigators themselves, should have conducted the inspection of the files to better protect any attorney-client relationships.