The Fourth Amendment protects U.S. citizens from unreasonable searches and seizures by government officials. In 1949, Dr. Julius Wolf was convicted of performing illegal abortions, but he claimed the evidence against him had been seized illegally, without a proper search warrant or probable cause. One of his former patients reported that she had gone to him for an abortion, and police entered his office without a warrant and seized an appointment book. The women in the book also reported that Wolf had performed abortions, and this evidence was used to convict him. When the case made it to the Supreme Court, it ruled 6-3 against Wolf. The heart of the matter was the federal exclusion rule, which discouraged improper search and seizure by ruling that all evidence collected illegally wasn't admissible in court. Wolf had run afoul of a state law, and the court decided that the exclusion rule didn't apply to states. The majority opinion felt that there were other, less restrictive methods to discourage illegal searches, and that neither the Fourth or 14th Amendments necessitated the exclusion rule.
Mapp v. Ohio was decided just 12 years later, in 1961. In that case, authorities searched DollRee Mapp's house for a fugitive -- with no proof of a proper warrant. Mapp reported that they waved a piece of paper at her that she couldn't identify as a warrant, and no actual warrant was ever produced. Police found a cache of pornography that violated Ohio's obscenity laws, and the woman was convicted of obscenity based on that evidence. The intervening 12 years had shown that the "other methods" of discouraging illegal search and seizure weren't working, so the Court reversed itself within a surprisingly short period of time.