In the United States, a no-knock warrant is a warrant issued by a judge that allows law enforcement officers to enter a property without immediate prior notification of the residents, such as by knocking or ringing a doorbell. In most cases, law enforcement will identify themselves just before they forcefully enter the property. It is issued under the belief that any evidence they hope to find can be destroyed during the time that police identify themselves and the time they secure the area, or in the event where there is a large perceived threat to officer safety during the execution of the warrant.
English common law has required law enforcement to knock-and-announce since at least Semayne's case (1604), and in Miller v. United States (1958), the Supreme Court of the United States recognized that police must give notice before making a forced entry. In the U.S. federal criminal law, the rule generally requiring knock-and-announce is codified at 18 U.S.C § 3109.
However, in Wilson v. Arkansas (1995) the Court created an exception to prevent the destruction of evidence and in Hudson v. Michigan (2006) the Court, by a 5-4 vote, held the exclusionary rule does not require the suppression of evidence police seize during an illegal forced entry.
According to the United States Department of Justice:
Federal judges and magistrates may lawfully and constitutionally issue "no-knock" warrants where circumstances justify a no-knock entry, and federal law enforcement officers may lawfully apply for such warrants under such circumstances. Although officers need not take affirmative steps to make an independent re-verification of the circumstances already recognized by a magistrate in issuing a no-knock warrant, such a warrant does not entitle officers to disregard reliable information clearly negating the existence of exigent circumstances when they actually receive such information before execution of the warrant.
No-knock warrants may be issued in every state except Oregon (where state law bans no-knock warrants) and Florida (in which a 1994 state supreme court decision prohibited no-knock warrants). 13 states have laws explicitly authorizing no-knock warrants and in twenty additional states no-knock warrants are routinely granted.
The number of no-knock raids has increased from 3,000 in 1981 to more than 50,000 in 2005, according to Peter Kraska, a criminologist at Eastern Kentucky University in Richmond. Raids that lead to deaths of innocent people are increasingly common; since the early 1980s, forty bystanders have been killed, according to the Cato Institute in Washington, D.C.
From 2010 through 2016, at least 81 civilians and 13 officers died during SWAT raids, including 31 civilians and eight officers during execution of no-knock warrants. Half of the civilians killed were members of a minority. Of those subject to SWAT search warrants, 42% are black and 12% are Hispanic. Since 2011, at least seven federal lawsuits against officers executing no-knock warrants have been settled for over $1 million.
No-knock warrants have been controversial for various reasons. There have been cases where burglars have robbed homes by pretending to be officers with a no-knock warrant. There have been many cases where armed homeowners, believing that they are being invaded, have shot at officers, resulting in deaths on both sides. While it is legal to shoot a homeowner's dog when an officer fears for his/her life, there have been numerous high-profile cases in which family pets lacking the size, strength, or demeanor to attack officers have been shot, greatly increasing the risk of additional casualties in neighboring houses via overpenetrating bullets.
In Cornelia, Georgia, a police informant alleged that he had bought $50 of methamphetamine from Wanis Thonetheva, a 30-year-old dealer at a residence belonging to Amanda Thonetheva, his mother. The dealer did not reside at the house, which contained no drugs or weapons, though a family with four young children lived in the house. Sheriff’s Deputy Nikki Autry secured a no-knock warrant after awaking a county magistrate at his home and making inaccurate sworn statements to him.
Police executed a no-knock, pre-dawn raid at 2:25am, with a SWAT team breaching a door with a ram and throwing a flash-bang stun grenade into a room with a 19 month old child. The grenade exploded inside the infant's crib, igniting the crib and his pillow, causing "blast burn injuries to the face and chest; a complex laceration of the nose, upper lip and face; 20% of the right upper lip missing; the external nose being separated from the underlying bone; and a large avulsion burn injury to the chest with a resulting left pulmonary contusion and sepsis"
The infant was placed in a medically induced coma, and needed a series of surgeries that cost more than a million dollars, becoming the subject of a lawsuit against the police department to pay medical bills. The legal case argued that children's toys, including a plastic child's pool were in the yard and the packaging for the play-pen the infant was sleeping in was next to the door the police breached, and the lawsuit alleges that police are "plainly incompetent" for failing to know that children were in the room.
The search yielded no drugs, no drug dealer and no weapons, and the drug dealer was arrested the next day without the use of flash-bang grenades.
The civil lawsuit was eventually settled, with the county paying $3.6 million, including approximately $1.65 million in pain and suffering. A Habersham County, Georgia grand jury declined to indict any of the participants, but did release a strongly worded report. Federal prosecutors then secured an indictment against Deputy Autry. She was acquitted of any wrongdoing by a federal jury after a weeklong trial.
- Kathryn Johnston (1914–2006) was an elderly Atlanta, Georgia, woman shot by three undercover police officers in her home on November 21, 2006, after she fired one shot at the ceiling, assuming her home was being invaded. While the officers were wounded by friendly fire, none of the officers received life-threatening injuries, but Johnston was killed by their gunfire.
- Two former Los Angeles Police Department officers, along with 13 others, have plead guilty to running a robbery ring, which used fake no-knock raids as a ruse to catch victims off guard. The defendants would then steal cash and drugs to sell on the street.
- Tracy Ingle was shot in his house five times during a no-knock raid in North Little Rock, Arkansas. After the police entered the house Tracy thought armed robbers had entered the house and intended to scare them away with a non-working gun. The police expected to find drugs, but none were found. He was brought to the intensive care, but police pulled him out of intensive care for questioning, after which they arrested him and charged him with assault on the officers who shot him.
- Ismael Mena was shot and killed by SWAT team officers in Denver, Colorado, who were performing a no-knock raid that was approved by a judge acting on false information contained in a search warrant. The police believed there to be drugs in the house, but no drugs were found on the premises, and it was later revealed that the address given to the SWAT team by officer Joseph Bini was the wrong one. Jefferson County District Attorney Dave Thomas investigated the matter and cleared the officers involved with the raid on the grounds that Mena had pointed a gun and fired it at SWAT officers, although who fired first remains in dispute. However, many have objected to the investigation's findings due to inconsistencies in the various officers' account of what happened. The American Civil Liberties Union, and others, have objected to the Denver Police Department's request for a no-knock raid and the judge's decision to allow such a raid on the grounds that they failed to meet the criteria necessary for a no-knock raid.
- A Georgia SWAT team shot and killed an armed homeowner, David Hooks, during a drug raid sparked by the word of a self-confessed meth addict and burglar who had robbed the property the previous day. David Hooks' wife, Teresa, looked outside and saw people with hoods on the evening of the raid and woke up her husband. Fearing the burglar or burglars who had struck two nights earlier had returned, Hooks armed himself. Despite the fact that the search warrant did not have a 'no knock' clause, the Drug Task Force and SRT members broke down the back door of the family's home and entered firing in excess of 16 shots. There is no evidence that David Hooks ever fired a weapon, nor was there any evidence he was involved in drugs. The Georgia Bureau of Investigation conducted an intensive 44-hour search of the property and came up with not one item of contraband.
- Hempstead, New York settled claims by Iyanna Davis for $650,000 after police in May 2010 shot her in the breast during their accidental execution of a no-knock warrant on the wrong address. Officer Michael Capobianco explained that he had unintentionally shot the 22-year-old woman after he tripped. Prosecutors did not file charges against the shooter.
- A Burleson County, Texas grand jury refused to indict Hank Magee for capital murder after he shot and killed a deputy sheriff inside his home during execution of a no-knock warrant on December 19, 2013.
- In Killeen, Texas, a grand jury indicted Marvin Louis Guy for capital murder after he shot and killed a police detective outside his home during execution of a no-knock warrant on May 9, 2014.
- In 2013, Tucson, Arizona agreed to settle claims by the family of Jose Guereña for $3.4 million after SWAT officers fired 71 shots in the seven seconds after their unannounced entry. Prosecutors did not file charges against the shooters.
- In December 2016, a jury in Corpus Christi, Texas acquitted Ray Rosas of attempted capital murder because it concluded that he was unaware the three home intruders he shot were SWAT officers. Prior to his acquittal, Rosas had spent 664 days in jail.
- In 2016, Framingham, Massachusetts agreed to settle claims by the family of Eurie Stamps for $3.75 million after SWAT officers shot the 68-year-old in the back while he was compliant and lying on his stomach. Prosecutors did not file charges against the shooter.
- In 2017, Paul Manafort was initially reported as the subject of a no-knock warrant in the 2017 Special Counsel investigation on Russian interference in the 2016 presidential elections. However these reports turned out to be false. 
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- United States v. McConney, 728 F.2d 1195, 1199 (9th Cir.) (en banc), cert. denied, 469 U.S. 824 (1984)
- Memorandum Opinion for the Chief Counsel, Drug Enforcement Administration, from Patrick F. Philbin, Deputy Assistant Attorney General for the Office of Legal Counsel, Re: Authority of Federal Judges and Magistrates to Issue "No-Knock" Warrants, 26 Op. O.L.C. 44 (June 12, 2002).
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- Epstein, Dimitri (2009). "Cops or Robbers? How Georgia's Defense of Habitation Statute Applies to No-Knock Raids by Police". Georgia State University Law Review. 26 (2): 5.