The Internal Revenue Service (IRS) (plaintiff) issued summons to two banks (defendants) for the records of John Gattuso, an individual whose tax liability the IRS was investigating. Federal law authorizes the IRS to examine books, papers, and records for the purpose of ascertaining the correctness of any return, making a return where none has been made, and determining the liability of any person for the internal revenue tax. The banks refused to comply with the summons, and the IRS sought enforcement in federal district court. The IRS attorney testified that he had not determined whether criminal charges were justified and had not made any reports or recommendations about the case to his superiors. Gattuso nonetheless argued that the investigation was “purely criminal.” The district court agreed with Gattuso, and held that the IRS had improperly attempted to pursue a civil investigation in order to obtain evidence for a criminal proceeding. The court of appeals affirmed. The case then came before the United States Supreme Court.