A search warrant is an important tool in a criminal case. This legal document, which is signed by a judge, grants law enforcement permission to conduct a physical search of a certain location to look for items that are specified. Before issuing a search warrant, the judge must evaluate whether law enforcement has established probable cause based on information they obtained from a reliable informant or from their own observations. Obtaining a warrant is a critical step in the investigative process -- if police officers conduct a search without a warrant, then in most cases, the search is presumed to be unreasonable. It is important to note that when the police are conducting a search, the search generally cannot extend beyond the scope that is specified in the search warrant -- meaning that the police cannot search beyond the location specified in the warrant nor can they look for other items that are not specified.