In order to obtain a search warrant in the United States, a law officer must appear before a judge or magistrate and swear or affirm that they have probable cause to believe that a crime has been committed. The officer is required to present their evidence and an affidavit to a magistrate, setting forth the evidence. "An affidavit must provide the magistrate with a substantial basis for determining the existence of probable cause." In other words, the law officer must present evidence, not merely their conclusions. "Sufficient information must be presented to the magistrate to allow that official to determine probable cause; his action cannot be a mere ratification of the bare conclusions of others."