In the case of Arroyo v. United States (1958), the U.S Supreme Court ruled in favor of the defendant, Mr. Arroyo, who was convicted for selling narcotics without a written order form from his buyer - an offense under federal law at that time. The court held that evidence obtained by federal officers through illegal search and seizure could not be used against him because it violated his Fourth Amendment rights which protect citizens from unreasonable searches and seizures. This decision reaffirmed previous rulings stating that any evidence acquired illegally is inadmissible in a criminal trial as per the exclusionary rule established to deter police misconduct.

In the dissenting opinion for Arroyo v. United States, Justice Whittaker argued that the majority misinterpreted Rule 48(a) of Federal Rules of Criminal Procedure which allows a court to dismiss an indictment or information with leave of court. He contended that this rule was designed to protect a defendant from harassment by repeated prosecutions for the same offense and not as a means for courts to deny government prosecutors' motions to dismiss charges they deem unwarranted. The justice believed it was inappropriate judicial overreach for judges to refuse dismissal based on their personal assessment about whether prosecution should proceed or not, especially when there's no evidence suggesting bad faith in prosecutor’s decision-making process. In his view, such refusal undermines separation-of-powers principles and infringes upon executive branch's constitutional authority over criminal prosecutions.