Such was the case in United States v. Dalton, in which the probable cause that initially supported the issuance of a warrant for the defendant’s home (in search of firearms and firearm paraphernalia) had dissipated before the officers ever executed the warrant.
The new information that vitiated the probable cause? The officers’ discovery that another individual--not the defendant--had been driving the defendant’s car when it evaded police and was later found harboring an AK-47. As a result of the new, intervening information, “at the time the officers executed the warrant, they had neither probable cause to believe that [the defendant] possessed the gun in his vehicle nor that he was illegally harboring firearms inside [the] house at that time." That search therefore violated the Fourth Amendment.
Dalton provides a cogent reminder for us that probable cause must exist not only when a warrant is issued, but also at the time the warrant is executed, and at all times during its execution.