In the case of Fredel Williamson v. United States, 1993, the U.S Supreme Court ruled on whether statements made by a co-conspirator could be used as evidence in court. The defendant, Fredel Williamson was convicted for drug trafficking based on testimonies given by his alleged accomplice who had died before trial and thus couldn't testify or be cross-examined. The lower courts allowed these statements to be admitted into evidence under Federal Rule of Evidence 804(b)(3), which allows hearsay exceptions for statement against interest if declarant is unavailable as a witness. However, upon appeal to the Supreme Court it was held that admitting such testimony violated Williamson's Sixth Amendment right to confront witnesses against him. The court stated that not all parts of an accomplice’s confession that incriminate a defendant are admissible; only those parts which are self-inculpatory (against speaker's penal interest) can be considered reliable enough for admission into evidence without violating confrontation clause rights. The ruling clarified how federal courts should interpret and apply Rule 804(b)(3). It also emphasized defendants' constitutional right to face their accusers in court even when dealing with hearsay exceptions.

In the dissenting opinion for Fredel Williamson v. United States, Justice Scalia disagreed with the majority's interpretation of Rule 801(d)(2)(E) of the Federal Rules of Evidence. He argued that a co-conspirator’s statement should be admissible as evidence only if it was made during and in furtherance of the conspiracy, not merely related to it. According to him, this rule has been misinterpreted by courts to mean that any statement made by a conspirator about the conspiracy is automatically admissible against all other members regardless of its purpose or timing. This broad interpretation could lead to misuse and potential prejudice against defendants who may have their guilt determined based on hearsay statements rather than direct evidence. Furthermore, he emphasized that such an approach contradicts both historical understanding and common-law tradition regarding hearsay exceptions for co-conspirators' statements.