The Exclusionary Rule: Definition, History, Pros & Cons

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  • 0:03 What Is the Exclusionary Rule?
  • 1:02 Exclusionary Rule Background
  • 2:22 The Fourth Amendment
  • 4:43 Fruit of the Poisonous Tree
  • 6:10 Exceptions and Catches
  • 7:08 Lesson Summary
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Lesson Transcript
Instructor: Mark Pearcy
The exclusionary rule is one of the most commonly-used (and famous) principles in U.S. criminal law. If evidence is illegally or unconstitutionally seized, it can't be used at trial - and this rule has changed the most basic ways in which the criminal justice system operates.

What Is the Exclusionary Rule?

Anyone who has watched a legal drama, whether on TV or in the movie theatre, has heard the phrase: 'the whole truth, and nothing but the truth.' The central idea behind the U.S. justice system is that an accused person is confronted by the evidence against him or her in an effort to discover the truth of an alleged crime.

But 'the truth' is a vague concept; and sometimes, serving the cause of truth doesn't include all the evidence. Since 1961, the U.S. court system has regularly used a rule which has affected hundreds, if not thousands, of criminal cases. In fact, it has largely changed the way law is practiced in America. It started with a case, Mapp v. Ohio, involving bomb-making, gambling and pornography, and it ended with the creation of the exclusionary rule, which simply says that any evidence which is illegally seized cannot be presented against a defendant at trial.

Exclusionary Rule Background

Though versions of the exclusionary rule existed in several U.S. states prior to 1961, it wasn't until that year that the rule was extended across the nation. That happened because of a colorful, odd case out of Ohio, involving a woman with the quirky name of Dollree Mapp. On May 23, 1957, police officers in Cleveland, Ohio, entered Mapp's home without her approval. They had received a tip that a suspect in a recent bombing could be found there. When they asked to enter the house, Mapp refused, citing her desire to see a search warrant (which the police didn't have). The police showed her a piece of paper (not a warrant), kicked in the door, and entered. There, they didn't find the bombing suspect; they did, however, find pornographic material, left by a prior tenant. That was enough to arrest Mapp: she was charged with possession of pornography (a crime in Ohio at that time) and convicted.

On appeal, Mapp's lawyers claimed that the warrant had been fake and that entering the home without legal justification was a violation of Mapp's constitutional rights. The Supreme Court, under Chief Justice Earl Warren, agreed, voting 6-3 in favor of Mapp.

The Fourth Amendment

The entire case (and thus, the exclusionary rule) revolves around the 4th Amendment to the U.S. Constitution, which says:

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.

What this means is that police who are looking for something - whatever it may be - have to have a search warrant describing what they're after and why. Without a warrant (or with one that is improperly done), whatever the police may find is excluded from trial.

This means that, in the case of Dollree Mapp, the pornography that was found should not have been presented at trial. And since that evidence was the reason she was arrested in the first place, the charges should have been dropped. The exclusion of the evidence removes the justification for the arrest. This happens all the time; and in fact, many criminal cases in America really begin with what's called a suppression hearing. This is when lawyers will meet with a judge to decide whether or not certain evidence can be presented at trial. Evidence that's deemed untrustworthy, unreliable, or prejudicial (or likely to lead the jury to an unwarranted conclusion) is left out; so, too, is evidence that can be shown to have been illegally seized.

You may be thinking, 'But wait! She actually did have pornography, which was against the law! That's evidence of a crime!' This would be true, but the 4th Amendment doesn't just protect people who have obeyed the law. The purpose of the Bill of Rights is to establish a set of principles that can't be violated by governments or their agents (in this case, the police). The exclusionary rule isn't part of the Bill of Rights; it was invented and applied by the U.S. Supreme Court as a method of enforcing the right guaranteed in the 4th Amendment to be free from unreasonable search and seizure. While the rule is often criticized (one such critic said the rule amounted to 'the criminal is to go free because the constable has blundered'), the Supreme Court has upheld the essential nature of the rule many times in the past.

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