In the case of Collier v. United States (1965), the Supreme Court examined whether a defendant could be convicted for both conspiracy to commit an offense and for committing the actual offense itself. The petitioner, Collier, was charged with conspiring to violate federal liquor laws and also with actually violating those same laws. He argued that this constituted double jeopardy - being tried twice for essentially the same crime - which is prohibited by the Fifth Amendment of U.S Constitution. The court held that a single act can give rise to distinct offenses if each statutory provision requires proof of different facts or elements not required by another. Therefore, it ruled against Collier's claim of double jeopardy because conspiracy to commit an offense and committing said offence are separate crimes requiring different evidence; one involves agreement between two or more people while other involves individual action. This decision clarified legal understanding around what constitutes 'the same offence' in terms of double jeopardy protections under US law.

In the dissenting opinion for Collier v. United States, Justice Harlan argued that the majority's decision to uphold a conviction based on evidence obtained through an unauthorized wiretap was inconsistent with previous Supreme Court rulings and violated Fourth Amendment protections against unreasonable searches and seizures. He contended that allowing such evidence would encourage law enforcement agencies to disregard constitutional safeguards in their investigations. Moreover, he disagreed with the majority's assertion that Congress had implicitly approved of using illegally obtained evidence by not explicitly prohibiting it in legislation. Instead, he believed this silence reflected uncertainty about how to address complex issues related to electronic surveillance rather than tacit approval of unconstitutional practices.