In Bourjaily v. United States, the Supreme Court ruled that a trial court could consider the contents of a co-conspirator's statements in determining whether those statements were admissible under Federal Rule of Evidence 801(d)(2)(E). The case involved an individual charged with conspiracy to distribute cocaine who sought to exclude from evidence incriminating phone calls between him and his alleged co-conspirator. He argued that these conversations should not be admitted unless there was independent proof of the conspiracy. However, the Supreme Court held that requiring independent evidence would be inconsistent with Congress’s intent when it adopted Rule 104(a), which allows judges to consider any relevant evidence when deciding preliminary questions about admissibility. Therefore, courts can use hearsay statements themselves as part of their determination on whether such statements are admissible as non-hearsay under Rule 801(d)(2)(E).

In the dissenting opinion for Bourjaily v. United States, Justice Brennan, joined by Justice Marshall, argued that the majority's decision to allow hearsay evidence under Rule 801(d)(2)(E) of the Federal Rules of Evidence without requiring independent corroborating evidence was a mistake. They contended that this ruling undermined traditional safeguards against unreliable testimony and could potentially lead to wrongful convictions based on uncorroborated hearsay. The justices also expressed concern about shifting too much power from juries to judges in determining what constitutes reliable evidence. Furthermore, they criticized the majority's interpretation of Rule 104(a), arguing it contradicted legislative intent and historical precedent which required independent proof for conspiracy before admitting co-conspirator statements into evidence.