Although the Fourth Amendment protects your privacy, the police may conduct a search of your home, barn, garage, car, boat, office, personal or business documents, bank account records, or other possessions, if:
Under the Fourth Amendment, as framed by the U.S. Supreme Court, “searches” have to be "reasonable." But not everything the police do to look for evidence qualifies as a Fourth-Amendment “search.”
According to the Supreme Court, law enforcement conducts a “search” when it, in an effort to find evidence or information:
If either of these happens, a search has occurred. And the search must have been reasonable in order to comply with the Fourth Amendment.
An example of a “trespass” search is the police installing a tracking device on the underside of a car in order to track its movements. The defendant’s movements in the car, on public roads, might not involve a reasonable expectation of privacy. Regardless, though, the attempt to gather information via physical intrusion qualifies as a “search.” (United States v. Jones, 132 S. Ct. 945 (2012).)
Determining whether a search occurred because the police violated a “reasonable expectation of privacy” has traditionally involved two questions:
When the answer to both questions is “yes”—and where the police violated the privacy expectation—a court will go on to consider the ultimate question: Was the search reasonable? (They'll also consider that question if there was a "trespass search.") If the search wasn’t reasonable, then any evidence it turned up probably won’t be admissible in court.
Consider public restrooms. Courts have come out both ways as to whether a user of a public bathroom had a reasonable expectation of privacy. In weighing the issue, courts have considered factors like:
In one case in Wisconsin, a court found that the defendant didn’t have a reasonable expectation of privacy where he used a locked gas station restroom for 25 minutes or more. He dozed off and didn’t respond to knocking. The court held that he didn’t have a right to challenge the “search” that happened when a police officer unlocked the door. The defendant had a right to expect privacy when first using the bathroom for its intended purpose, but he essentially forfeited that right. (The court noted that the gas station had a key to the bathroom, that the defendant didn’t have the right to keep others out for so long, and that the defendant didn’t respond to the officer’s knocking in a way to protect his privacy.) (State v. Neitzel, 758 N.W.2d 159 (2008).)
Let’s assume that a “search” occurred, and that it violated the law for any of a number of reasons. Perhaps:
The next issue is whether the evidence has to be kept out of court. In many instances, if it does, then the prosecution essentially has no case against the defendant. For instance, if someone is prosecuted for drug possession, but the only evidence of that possession came from the police illegally searching her, then the government will probably have to drop the case.
In Mapp v. Ohio, the U.S. Supreme Court established what's known as the “exclusionary rule.” (367 U.S. 643 (1961).) This rule provides that items seized in violation of the Fourth Amendment cannot be used as evidence against a defendant in a criminal prosecution. To this day, some commentators criticize the Mapp case on the ground that it unfairly “lets the criminal go free because the constable has erred.” In fact, in the time since Mapp, the Supreme Court has taken some of the bite out of the exclusionary rule. For example, evidence is often admissible where there appears to be a lawful basis for a search, but isn’t.
Defendants who believe that the police conducted an illegal search will want to challenge the search in court, to argue that what turned up should not be admitted at trial. The rules that determine the legitimacy of searches and seizures are complex, and the law varies somewhat from state to state, making a criminal defense attorney critical. The rules aren’t set out neatly in statutes or regulations. Rather, arguments that a search is illegal usually have to be pieced together from a number of appellate court decisions involving similar facts. Moreover, in many states, a special body of rules governs the procedures for challenging the legality of a search. For example, a defendant may have to challenge a search in a special proceeding before trial or lose the right to do so.