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. (You can find it and other amendments in the Bill of Rights in Nolo's list of The Most Important Cases, Speeches, Laws & Documents in American History.)
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 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.
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:
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).)
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 that 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 seize 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.)
Officer Wiley arrests Hy Lowe for selling phony telephone cards. A judge rules that Officer Wiley illegally entered Lowe's home and improperly seized a map showing the location where Lowe hid the phone cards. Officer Wiley then found the phone cards in that location. Because Officer Wiley obtained the map through an illegal search, it and the phone cards are inadmissible. The phone cards are the fruit of the unlawful search.
Not always end of story. 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.
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.