Shaw v. United States was a United States Supreme Court case that addressed 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 Shaw who was accused of stealing a horse. The police searched Shaw's home without a warrant and found evidence of the crime. Shaw argued that the evidence should not be used against him because it was obtained through an illegal search and seizure. The Supreme Court ruled in favor of Shaw, holding that evidence obtained through an illegal search and seizure could not be used against a defendant in a criminal trial. The Court reasoned that the Fourth Amendment of the United States Constitution protects citizens from unreasonable searches and seizures, and that the evidence obtained in this case was obtained in violation of that amendment. The Court also noted that the exclusionary rule, which prohibits the use of illegally obtained evidence in criminal trials, was necessary to protect citizens from unreasonable searches and seizures. The decision in Shaw v. United States established the exclusionary rule as a cornerstone of Fourth Amendment jurisprudence. The Court's ruling has been cited in numerous cases since then, and it remains an important precedent in criminal law.

Justice Field delivered the dissenting opinion in Shaw v. United States, arguing that Congress did not have the power to pass a law which would allow for an individual's conviction without proof of criminal intent. He argued that this was a violation of due process and fundamental fairness as it allowed for individuals to be convicted on circumstantial evidence alone, even if they had no knowledge or intention of committing any crime. Furthermore, he noted that such laws could lead to arbitrary convictions and punishments based solely on suspicion rather than actual guilt. Justice Field concluded by stating that while Congress may have been attempting to protect citizens from harm through such legislation, it should not come at the expense of constitutional rights and protections guaranteed under the Constitution.