Officers’ fifteen to twenty second wait before making forcible entry to serve a search warrant was sufficient under the Fourth Amendment. The officers here knocked and announced their purpose and identity, waited for fifteen to twenty seconds, and then broke open the door. The Ninth Circuit had held that absent exigent circumstances, the destruction of property is permissible only if there has been an explicit refusal of admittance or a longer time lapse than was at issue here. The Supreme Court reversed, holding first that the standards governing when officers can legitimately enter after knocking are the same as those governing when officers can dispense with knocking and announcing altogether. The obligation to knock and announce gives way when officers have reasonable grounds to expect futility or to suspect that an exigency will arise as soon as they announce their presence. After fifteen to twenty seconds without a response, the officers could reasonably suspect that contraband would be “flushed away” if they continued to wait. The relevant inquiry was limited to what the officers knew prior to making entry, and the issue was how long it would reasonably take the suspect to dispose of the drugs, not how long it would reasonably take him to answer the door. Thus, the fact that the defendant was in the shower and could not get to the door within twenty seconds was not relevant to the court’s inquiry.