The Supreme Court case Mesarosh, Alias Nelson, et al. v. United States in 1956 involved a group of individuals who were convicted under the Smith Act for advocating and teaching the violent overthrow of the U.S government. The defendants appealed their convictions on several grounds including that they had been denied due process because one of the key witnesses against them was found to be unreliable by the FBI after their trial concluded. The Supreme Court unanimously overturned their convictions and ordered a new trial stating that it would not allow an American citizen to go to jail based on false testimony even if there is enough other evidence to support conviction. This decision emphasized that justice must be done both in substance and procedure; any hint of perjury or unreliability could taint an entire prosecution's case.

In the dissenting opinion for Mesarosh v. United States, Justice Frankfurter argued that the majority's decision to remand the case back to district court was unnecessary and potentially harmful. He contended that while it is essential for courts to ensure justice and fairness in all proceedings, there were no substantial grounds or new evidence presented which would warrant a retrial of this case. The only basis for such action was an unrelated perjury charge against one government witness - something he believed did not undermine his testimony in this particular trial or affect its outcome significantly. Moreover, he expressed concern about setting a precedent where any subsequent discrediting of a prosecution witness could lead to overturning convictions long after they have been finalized; thus undermining legal certainty and finality.