A judge reviewing an application to search a premises, vehicle, or person considers whether the affidavit of probable cause, which is a sworn statement by a police officer or other law enforcement official that probable cause exists to conduct the search, represents a credible presentation of evidence, and that the evidence presented does in fact constitute "probable cause" that a crime can be linked to the person or location for which the search warrant is sought. While this may appear tautalogical, the judge knows better than most that the viability of any prosecution resulting from the execution of the search warrant hinges on the credibility of the affidavit.
In the event that a criminal trial commences, and that evidence vital to the prosecution's case was attained as a result of a search warrant that originated with an affidavit of probable cause, both the prosecutor and the judge need to be confident in the integrity of the process by which the search warrant was requested and executed. In order to prevent a case from proceeding to trial without proper diligence with regard to the attainment of evidence, the judge reviewing the affidavit both reviews the document carefully and queries the police officer or other official requesting the warrant to increase his or her level of confidence that the search is in fact warranted by the facts. Barring that level of confidence, the judge will deny the warrant.