Knock and Announce

Richardson v. Wisconsin (1997)

A forcible entry is permissible after ∆ opens the door and sees police and the police reasonably believes the ∆ will destroy evidence.

Wilson v. Arkansas (1995) (Constitutional)

A knock and announce isn't necessary when police have reason to believe a crime is being commited, if the defendant has been convicted of and committed a crime, or when the police reasonably believe there will be a destruction of evidence under the circumstances. There is no per se rule exempting the knock and announce requirement in drug cases.

Halberstam

A search incident to arrest is permissible without probable cause.

U.S. v. Banks (2003)

A wait time of 15 to 20 seconds is a reasonable amount of time for an officers to wait after a knock to procede with a forcible entry.

Wilson v. Arkansas (1995)

Even if police have a search warrant based on probable cause, they first must knock and announce that they have a warrant (even if the door is unlocked)