Unreasonable searches and seizures are prohibited by the

Rules governing searches and seizures by the police or other law enforcement agents arise from the Fourth Amendment to the U.S. Constitution. This provision protects the privacy rights of citizens against excessive intrusions by the government. However, law enforcement has a right to conduct searches and seizures that are reasonable. A search or seizure is reasonable if the police have a warrant from a judge based on probable cause to believe that a suspect has committed a crime. Also, a search may be reasonable without a warrant if an exception applies under the circumstances. The Fourth Amendment does not protect citizens from searches by private security guards, unless they are acting for or with the police.

Protections under the Fourth Amendment apply only to items and locations in which a citizen has a legitimate expectation of privacy. Determining whether an expectation of privacy existed requires a court to consider subjective and objective expectations. In other words, it must decide whether the person actually expected privacy and also whether a reasonable person would expect privacy. There is no expectation of privacy when an item or location is in plain view, while there may be a strong expectation of privacy in a person’s home or in a space that society traditionally considers to be private, such as a restroom.

The Exclusionary Rule

There are two main legal doctrines that can apply when a search or seizure violates the Fourth Amendment. The first is known as the exclusionary rule. It provides that any evidence obtained through an unreasonable search or seizure cannot be introduced against a defendant at a criminal trial. The defendant or their attorney will need to bring a motion to suppress this evidence, though, rather than relying on the judge to exclude it automatically. Sometimes the prosecution depends heavily on the evidence from the search to prove its case, so a successful motion to suppress may defeat the case altogether.

It may seem counterintuitive or unnecessarily lenient to allow a defendant to escape liability for a crime that they committed, based on a procedural error. The justification for the exclusionary rule is that the police would have an incentive to conduct unconstitutional searches and seizures if they could introduce the evidence anyway. This would undermine the privacy of many citizens. Certain exceptions to the exclusionary rule also limit its scope.

As with most legal rules, there are exceptions to the exclusionary rule. For instance, the exclusionary rule generally does not apply to violations of the knock-notice rule unless a particular state has decided differently.

The prosecution sometimes can use the unconstitutionally seized evidence to impeach the credibility of the defendant as a witness at trial. If the prosecution is able to get a conviction without that evidence, the judge may still consider the evidence in determining the sentence. It also may be admissible in a deportation proceeding against the defendant in the immigration system.

Fruit of the Poisonous Tree

The second main doctrine in the search and seizure context affects evidence that is obtained because law enforcement obtained the unconstitutionally seized evidence. This evidence also is not admissible against the defendant under the fruit of the poisonous tree doctrine. (The idea is that the tree is the unconstitutionally seized evidence, and the fruit is the evidence obtained through it.)

The fruit of the poisonous tree doctrine may affect multiple pieces of evidence. For example, Officer Bill stops Megan without cause, searches her purse, and finds a note indicating that she is hiding stolen property in her closet. Officer Bill enters Megan’s apartment, seizes the stolen property, and arrests Megan for theft. Neither the note nor the hidden property is admissible evidence because the search of Megan’s purse was illegal (the poisonous tree), and the seizure of the hidden property (the fruit) resulted from the illegal search.

An exception to the fruit of the poisonous tree doctrine applies when law enforcement would have found the evidence anyway. Also, if an officer does not have a legitimate reason to stop and search someone, but a legitimate reason arises during the stop, evidence that they find may be admissible in some situations. There is another exception for voluntary statements by defendants that are provided without Miranda warnings. While the statements cannot be admitted because of the Miranda violation, evidence obtained from the statements can be admitted.

Last reviewed October 2022

Learn when the government can invade your privacy to hunt for evidence of a crime.

The Fourth Amendment to the U.S. Constitution places limits on the power of the police to make arrests, search people and their property, and seize objects and contraband (such as illegal drugs or weapons). These limits are the bedrock of search-and-seizure law. This article covers basic issues you should know, beginning with an overview of the Fourth Amendment itself.

The Fourth Amendment: Protecting Your Privacy

The Fourth Amendment to the U.S. Constitution reads as follows:

"The right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures, shall not be violated, and no Warrants shall issue, but upon probable cause, supported by Oath or affirmation, and particularly describing the place to be searched, and the persons or things to be seized."

The search-and-seizure provisions of the Fourth Amendment are all about privacy. To honor this freedom, the Fourth Amendment protects against "unreasonable" searches and seizures by state or federal law enforcement authorities.

The flip side is that the Fourth Amendment does permit searches and seizures that are reasonable. In practice, this means that the police may override your privacy concerns and conduct a search of you, your home, barn, car, boat, office, personal or business documents, bank account records, trash barrel, or whatever, if:

• the police have probable cause to believe they can find evidence that you committed a crime, and a judge issues a warrant, or
• the particular circumstances justify the search without a warrant first being issued.

When the Fourth Amendment Doesn't Protect You

The Fourth Amendment applies to a search only if a person has a "legitimate expectation of privacy" in the place or thing searched. If not, the amendment offers no protection because there are, by definition, no privacy issues.

Legitimate Expectation of Privacy

Courts generally use a two-part test (fashioned by the U.S. Supreme Court) to determine whether, at the time of the search, a defendant had a legitimate expectation of privacy in the place or things searched:

• Did the person actually expect some degree of privacy?
• Is the person's expectation objectively reasonable—that is, one that society is willing to recognize?

For example, a person who uses a public restroom expects not to be spied upon (the person has an expectation of privacy), and most people—including judges—would consider that expectation to be objectively reasonable. Therefore, the installation of a hidden video camera by the police in a public restroom would be considered a "search" and would be subject to the Fourth Amendment's requirement of reasonableness.

On the other hand, if an officer stops a car and, when talking to the driver, happens to notice a weapon on the passenger seat, there's been no search under the Fourth Amendment. That's because, even if the driver somehow considered the passenger seat to be a private place, society isn't willing to extend privacy protections to that particular location. In other words, there's no objectively reasonable expectation of privacy with respect to the gun because it was in plain view.

A good example of how this works comes from a U.S. Supreme Court case in which the court held that a bus passenger had a legitimate expectation of privacy in an opaque carry-on bag positioned in a luggage rack above the passenger's head. The Court held that the physical probing by the police of the bag's exterior for evidence of contraband constituted a search subject to Fourth Amendment limitations. (Bond v. U.S., 529 U.S. 334 (2000).)

What Happens When a Search Violates the Fourth Amendment

If it turns out the police conducted an illegal search, does that mean the criminal case is over? Not necessarily, but consequences do exist.

The Exclusionary Rule

If, upon review, a court finds that an unreasonable search occurred, any evidence seized as a result of it cannot be used as direct evidence against the defendant in a criminal prosecution. This principle, established by the U.S. Supreme Court in 1961, has come to be known as the exclusionary rule.

To this day, many commentators criticize the exclusionary rule on the ground that it unfairly "lets the criminal go free because the constable has erred." But the rule's supporters argue that excluding illegally seized evidence is necessary to deter police from conducting illegal searches. According to this deterrence argument, the police are less likely to conduct improper searches if the resulting evidence can't be used to convict the defendant. (There are, however, exceptions to the exclusionary rule—for one, see Police Searches and the Good Faith Exception.)

Fruit of the Poisonous Tree Doctrine

Not only is evidence that's the product of an illegal search generally inadmissible in court, but so too is additional evidence derived from the initial evidence. This principle is colorfully known as the "fruit of the poisonous tree" doctrine. The "tree" is the evidence that the police illegally seized in the first place; the "fruit" is the second-generation product of the illegally seized evidence. Both tree and fruit are typically inadmissible at trial. (For more, see Fruit of the Poisonous Tree.)

Impact on the Criminal Case

Some defendants believe that if they can show that a search was illegal, the case must be dismissed. Not true. If a prosecutor has enough other evidence to prove the defendant guilty, the case can continue. Also, the illegally-seized evidence can generally be considered by a judge when deciding on an appropriate sentence following conviction and admitted in civil and deportation cases. In some circumstances, a prosecutor can use such evidence to impeach (attack the credibility of) a defendant who testifies at trial.

More Information

To learn more about search-and-seizure law, get The Criminal Law Handbook: Know Your Rights, Survive the System, by Paul Bergman (Nolo). If you might need to talk to a criminal defense attorney or want to know how the law may differ slightly in your state, you can turn to Nolo's trusted Lawyer Directory to find a lawyer near you.