Should law enforcement wait too long after issuance of a search warrant to make the actual search, the warrant may become stale. Defendants may challenge a stale search warrant as insufficient to show probable cause; a successful challenge of this kind will render the evidence seized inadmissible in court. Those who believe themselves possible objects of a stale search warrant should seek legal advice.
Under the Fourth Amendment, any government-conducted search requires issuance of a search warrant by a court. A valid search warrant must state "with particularity" the place to be searched and the items being sought in the search. The judge who issues the warrant must also be "neutral and detached," meaning that the judge has no reason or incentive to issue the warrant beyond the evidence presented in the warrant application.
Courts issue search warrants based on a finding of probable cause to search. Probable cause to search exists when, based on all information presented by the law enforcement officer to the court, the court has reason to believe that the location to be searched will contain evidence of commission of a crime, or the fruits of that crime. Probable cause is also temporal; the object of the search must be likely to be found there at the approximate time at which the search will take place.
A search conducted pursuant to a valid warrant may still be found illegal if the warrant is improperly executed. Officers who execute the search warrant cannot exceed the warrant's scope, meaning that they cannot search areas outside the scope of the warrant. Officers also may not wait too long between issuance of the warrant and execution (unless the delay is reasonable), or the warrant will be "stale". A stale search warrant is subject to challenge by the defendant as no longer supported by probable cause. Analysis of staleness takes into account subjective factors, but courts generally find search warrants stale 10 days after issuance.
Staleness analysis changes slightly in the context of anticipatory warrants. A court grants an anticipatory warrant when an object is not yet on the premises to be searched, but will be there at some future point in time. An anticipatory warrant must be executed at that future point in time. Officers use anticipatory warrants when, for instance, they expect the defendant to receive a package containing contraband on a specific future date. Because anticipatory warrants, by their very nature, imply some delay in execution, courts will often analyze the staleness of anticipatory warrants on a case-by-case basis.
Certain exceptional situations may overcome the invalidity of a search warrant. When officers have a good-faith, reasonable belief that the search warrant is valid (for instance, when the date on the warrant itself is incorrect and the officers executing the warrant have no idea of the correct date for which the warrant was meant to be issued, and they execute search on the incorrect date), that good-faith belief may render the evidence seized admissible despite the invalid warrant.