Many years later at the state level in the 1961 landmark case of Mapp v. Ohio, the U.S. Supreme Court expanded the rights of the accused by applying the exclusionary rule to both federal and state criminal trials. Ms. Mapp had been sentenced to a year in jail for possessing pornographic materials seized in a search of her apartment. The police entered her apartment without a valid warrant. The state attorneys argued that no matter how incorrectly the police behaved, their actions did not change the facts in the case. Ms. Mapp was guilty of possessing pornographic materials and her conviction should stand. The State also argued that the U.S. Supreme Court should allow local government to handle police excesses in their own way. The Supreme Court disagreed with the state of Ohio and would not accept such an abuse of power exhibited by the Cleveland police. The Court's decision ensured that all citizens were afforded Fourth Amendment protection against "unreasonable searches and seizures" by all levels of governmental officials.
In circumstances when the court finds that an illegal search occurred, any evidence seized as a result of the search cannot be used as direct evidence against the defendant in a criminal prosecution. To this day, many people criticize it on the ground that it unfairly lets the criminal go free because the law has erred. In contrast supporters of the exclusionary rule argue that excluding illegally seized evidence is necessary to deter police from conducting illegal searches. According to the deterrence argument, the police will not conduct improper searches if the resulting evidence cannot be used to convict the defendant. Some defendants falsely believe that if they can show that a search was illegal, the case must be dismissed. If a prosecutor has enough other evidence to prove the defendant guilty, the case can continue. Also, the illegally seized evidence can be considered by a judge when deciding on an appropriate sentence following conviction and admitted in civil cases.