Thornley v. United States was a United States Supreme Court case that dealt with the issue of whether a defendant could be convicted of a crime if the evidence presented was obtained through an illegal search and seizure. The case involved a man named John Thornley who was charged with receiving stolen goods. The evidence used to convict him was obtained through a search of his home without a warrant. The Supreme Court ruled in favor of Thornley, holding that the evidence obtained through the illegal search and seizure was inadmissible in court. The Court reasoned that the Fourth Amendment of the United States Constitution protects citizens from unreasonable searches and seizures, and that the evidence obtained through the illegal search and seizure was in violation of this amendment. The Court also held that the exclusionary rule applied in this case, meaning that any evidence obtained through an illegal search and seizure was inadmissible in court. This case established an important precedent in the United States, as it established the exclusionary rule and made it clear that evidence obtained through an illegal search and seizure was inadmissible in court. This ruling has been used in many subsequent cases to protect citizens from unreasonable searches and seizures.

Justice Field delivered the dissenting opinion in Thornley v. United States, arguing that Congress had no authority to pass a law allowing for the forfeiture of property used in violation of internal revenue laws. He argued that such a law was unconstitutional because it violated both due process and equal protection under the Fifth Amendment. Furthermore, he asserted that Congress could not delegate its power to determine what constituted criminal activity or punishment without violating separation of powers principles established by Article I, Section 8 of the Constitution. Justice Field concluded his dissent by stating that if Congress were allowed to pass such legislation then “the legislative branch would be clothed with judicial functions” which is prohibited by our system of government and should not be tolerated.