Sweeny v. United States was a Supreme Court case that addressed the issue of whether a person could be convicted of a crime if the evidence used to convict them was obtained through an illegal search and seizure. The case involved a man named John Sweeny, who was accused of stealing a horse. The evidence used to convict him was obtained through a search of his home without a warrant. The Supreme Court ruled in favor of Sweeny, finding that the evidence used to convict him was obtained illegally and could not be used in court. The Court held that the Fourth Amendment of the Constitution protects citizens from unreasonable searches and seizures, and that evidence obtained through an illegal search and seizure could not be used in court. This ruling established the exclusionary rule, which states that evidence obtained through an illegal search and seizure cannot be used in court.

In the case of Sweeny v. United States, the Supreme Court was asked to decide whether a defendant who had been convicted in a criminal trial could be retried after his conviction had been reversed on appeal. The majority opinion held that such retrials were permissible under certain circumstances, but Justice Field dissented from this ruling. He argued that allowing retrials would violate the Double Jeopardy Clause of the Fifth Amendment and deprive defendants of their right to due process by subjecting them to multiple trials for the same offense. Furthermore, he noted that there was no precedent for permitting such retrials and warned against creating an exception which could lead to further abuses down the line. In conclusion, Justice Field believed that allowing these types of retrials would undermine fundamental principles of justice and fairness enshrined in our Constitution.