The conclusion that the Supreme Court reached in this case was that any evidence that is obtained by an illegal search or seizure is inadmissible in state courts. This case applied the exclusionary rule to the states. It had previously applied to the federal government but not to the states.
In this case, police believed that a suspect in a bombing was hiding in Dollree Mapp’s house. They did not get a warrant, but entered the home anyway, disregarding Mapp’s demands that they get a warrant in order to search her home. The police did not find the suspect but did find material that, at that time, violated Ohio’s laws against obscenity. Mapp was convicted of possession of obscene material but appealed her conviction in part on the basis that the material had been found in an illegal search.
Prior to this, the Supreme Court had held that the 4th Amendment did apply to the states. This meant state police officers had to get warrants to search a home just as federal officials would. But the Court had not yet applied the exclusionary rule to the states. In this case, they concluded that that rule should apply to the states. The Court concluded that it was unjust to allow states to use evidence found in illegal searches to convict a person.