In the case of Mesarosh, Alias Nelson, et al. v. United States (1956), the Supreme Court unanimously overturned a previous conviction of five men accused of advocating for violent overthrowing of the U.S government under the Smith Act due to perjury by a key prosecution witness. The defendants were members or affiliates of Communist Party USA and had been convicted in 1949 based on testimonies from several witnesses including an FBI informant named Harvey Matusow who later admitted that he lied during his testimony at their trial as well as others'. The court ruled that it was not fair to let stand convictions which may have been influenced by false testimony, even if there might be enough other evidence to support them. This decision emphasized justice over procedural correctness and highlighted concerns about potential abuses in anti-communist prosecutions during this period.

In the dissenting opinion for Mesarosh v. United States, Justice Tom C. Clark argued that the majority's decision to remand the case back to district court due to unreliable testimony from a government witness was unnecessary and could set a dangerous precedent. He contended that it is not within the Supreme Court's jurisdiction or duty to assess credibility of witnesses, which should be left up to juries in lower courts. Furthermore, he expressed concern about potential implications on future cases where verdicts might be overturned based on post-trial revelations about witness credibility - an issue he believed would undermine public confidence in judicial proceedings and disrupt legal finality.