Where the warrant was executed in the early morning hours when everyone would likely be asleep, a five-second pause between the knock-notice and entry was not sufficient to satisfy 18 U.S.C. § 3109, the federal knock-notice statute. Moreover, the record contained only generalizations and no specific information that appellant would be armed or dangerous to justify entry under exigent circumstances. The Court of Appeals reversed the district court’s denial of appellant’s suppression motion.