In the 1907 case of Williamson v. United States, the U.S. Supreme Court ruled on a matter concerning self-incrimination and due process rights under the Fifth Amendment. The defendant, Williamson, was convicted for conspiring to defraud the government based largely on testimony from co-conspirators who were not present in court for cross-examination. On appeal, he argued that this violated his constitutional rights as it denied him an opportunity to confront those accusing him directly - a key aspect of due process law. The Supreme Court disagreed with Williamson's argument and upheld his conviction by ruling that statements made by co-conspirators during their conspiracy could be used against them even if they weren't available for cross-examination at trial. This decision established important precedent regarding hearsay exceptions and confrontation clause issues within criminal trials.

In the dissenting opinion for Williamson v. United States, Justice Harlan argued that the court erred in allowing a co-conspirator's confession to be used as evidence against another conspirator after the conspiracy had ended. He contended that such confessions are inherently unreliable and should not be admissible unless made during the course of and in furtherance of the conspiracy itself. Furthermore, he believed it was improper for a trial judge to instruct jurors on how they could use this kind of testimony without first determining its admissibility outside their presence. This approach, according to him, unfairly prejudiced defendants by exposing jurors to potentially inadmissible evidence before any determination about its validity was made.