The law that governs search warrants is based on the guarantees of the Fourth Amendment to the US Constitution. According to it, law enforcement officers must announce their presence and provide residents with the opportunity to open the door before a search. The objectives of the Knock-and-Announce Requirement are as follows:
- To prevent violence against police or other persons on the premises;
- To prevent the privacy of people in the room from unforeseen circumstances;
- To prevent material damage;
- To allow the tenant to review the order and point out a possible erroneous address or other errors.
A statement of the identity of a law enforcement officer and the presence of a search warrant is usually sufficient. Failure to comply with this rule without any pressing circumstances may make the search unreasonable under the constitution. An example is when the police entered a house before announcing their presence and purpose; the court ruled a violation of the requirement.
In urgent circumstances, the searchers may use any method to enter the premises, guided by reasonable reasons. There is no need to comply with this requirement when the circumstances pose a threat of violence or there is reason to believe that the evidence will be destroyed during knocking and warning. This is relevant when footsteps, whispers, or toilet flushes are heard, indicating a possible escape or destruction of evidence; it can create a pressing circumstance justifying immediately forced entry. Penetration without announcement is also applicable in cases where:
- The suspect had a violent conviction, was armed, and the police suspected that he knew that the police were investigating him;
- Police saw smoke and smelled explosives;
- Police suspected the accused had a rocket launcher inside the premises for a search;
- The police noticed the suspect leaving the apartment through the back door.
Even if the Knock-and-Announce Requirement is justified, the police must still act reasonably, or evidence will be ruled out.
