An unindicted co-conspirator, or unindicted conspirator, is a person or entity that is alleged in an indictment to have engaged in conspiracy, but who is not charged in the same indictment. Prosecutors choose to name persons as unindicted co-conspirators for a variety of reasons including grants of immunity, pragmatic considerations, and evidentiary concerns.
The United States Attorneys' Manual generally recommends against naming unindicted co-conspirators, although their use is not generally prohibited by law or policy. Some commentators have raised due-process concerns over the use of unindicted co-conspirators. Although there have been few cases on the subject, the Fifth Circuit Court of Appeals addressed these concerns in United States v. Briggs.
The term unindicted co-conspirator was familiarized in 1974 when then U.S. President Richard Nixon was named as an unindicted co-conspirator in indictments stemming from the Watergate Investigation. Nixon was not indicted due to concerns about whether the United States Constitution allowed the indictment of a sitting President (see Executive privilege).