Writing for the Court, Justice John Paul Stevens held that a search conducted pursuant to a search warrant that fails to describe the items to be seized is “plainly invalid” and clearly “unreasonable” under the Fourth Amendment, emphasizing that search warrants must “particularly describ[e] . . . the persons or things to be seized.” Because Groh conceded that the warrant didn’t describe the type of evidence sought and instead had only a description of the house in the space reserved for items to be seized, Stevens found that the warrant “did not describe the items to be seized at all.” Consequently, Stevens established that a search executed under such a glaringly defective document is “so obviously deficient that we must regard the search as ‘warrantless’ within the meaning of our case law,” meaning the entry into the Ramirez’s ranch “presumptively unreasonable.”

Stevens rejected the government’s argument that an adequate description in the supporting warrant application or affidavit can save a facially invalid warrant, writing that the Fourth Amendment “requires particularity in the warrant, not in the supporting documents.” Stevens explained that while a warrant may cross-reference supporting papers if it uses “appropriate words of incorporation” and the supporting document accompanies the warrant, no such incorporation or attachment took place in Ramirez’s case because the affidavit remained sealed. Stevens emphasized that the particularity requirement doesn’t merely prevent general searches but also “assures the individual whose property is searched or seized of the lawful authority of the executing officer, his need to search, and the limits of his power to search.”

Turning to qualified immunity under Saucier v. Katz, Stevens explained that immunity depends on “whether it would be clear to a reasonable officer that his conduct was unlawful in the situation he confronted.” He added that under United States v. Leon, “a warrant may be so facially deficient . . . that the executing officers cannot reasonably presume it to be valid.” Here, Stevens reasoned that because Groh prepared the warrant himself, he couldn’t reasonably rely on the magistrate’s signature or a claim ignorance of a “glaring deficiency that any reasonable police officer would have known was constitutionally fatal.”

Applying these principles to Groh’s search of the Ramirez’s ranch, Stevens found that Groh conducted an unconstitutional search and was not entitled to qualified immunity. Stevens explained that while Groh detailed the stockpiled firearms and explosives in his affidavit, he mistakenly typed a description of the ranch in the warrant’s itemization block, leaving the warrant without any reference to the specific evidence sought. Stevens also found that Groh’s alleged oral statements to Mrs. Ramirez during the search couldn’t cure the constitutional defect, because her account showed that Groh stated only that he was looking for “an explosive device in a box,” which he described as “little better than no guidance at all.” Ultimately, Stevens concluded that “even a cursory reading of the warrant in this case—perhaps just a simple glance—would have revealed a glaring deficiency,” holding that Groh violated the Ramirez’s Fourth Amendment rights and denying him qualified immunity.