Final answer:
The Fourth Amendment's protections against unreasonable search and seizure apply at the investigation stage, before someone is charged with a crime, and require law enforcement to have probable cause or adhere to exceptions for a legal search.
Step-by-step explanation:
The Fourth Amendment's protections against unreasonable search and seizure apply primarily during the investigation stage of the criminal justice system, that is, before a person has been charged with a crime. Landmark cases, such as Mapp v. Ohio and Katz v. United States, have affirmed that evidence obtained in violation of the Fourth Amendment is inadmissible in court, and that these protections extend to anywhere a person has a 'reasonable expectation of privacy.'
The amendment requires law enforcement to obtain a search warrant, backed by probable cause, although there are some exceptions, such as exigent circumstances, consent, and items in plain view. Public school officials also have the authority to conduct searches under New Jersey v. T.L.O., but they are held to a lower standard of reasonable suspicion rather than probable cause.