In Messerschmidt v. Millender, published February 22, 2012, the U.S. Supreme Court reversed an en banc 9th Circuit decision that a police officer was not entitled to qualified immunity for carrying out a search under a warrant. The warrant was issued after the suspect's victim told police that the suspect was trying to kill her with a particular weapon, that he threatened her because she called the police on him, and that he was in a street gang. The warrant application called for search and seizure of all firearms and firearm-related items in the suspect's residence, along with all gang-related materials. The application was approved by the officer's superior and the district attorney. A magistrate issued the warrant. The officer seized a firearm from the persons at the residence, although the suspect was not there. The persons at the residence then sued the officer for violation of the 4th Amendment. The en banc 9th Circuit held that a warrant that called for seizure of all firearms (not just the one used in the crime) and gang materials was so obviously overbroad that no reasonable officer could have believed it valid; and ruled that the officer was not entitled to qualified immunity.
The Supreme Court majority agreed that an officer cannot rely on a warrant that is so deficient that no reasonable officer could rely on it, and will not be entitled to qualified immunity for relying on such a warrant. But that is a rare exception to the rule that an officer who relies on a warrant approved by a neutral magistrate will generally be entitled to qualified immunity. In particular, since this warrant contained only correct facts, did not omit material facts, and was approved by a superior, a prosecutor, and a neutral magistrate, a reasonable officer could have believed that the warrant was proper. The majority did not rule on whether the warrant was in fact proper. One concurring justice concluded the warrant was proper; another justice concluded that an officer could reasonably believe the warrant was proper as to the fireams but not as to the gang materials; and two justices dissented from the ruling.