If you've been a fan of legal shows over the years, from "Perry Mason" to "Law and Order," you may have heard of a legal doctrine called "fruit of the poisonous tree." The term sounds rather exotic. However, it basically means that evidence obtained illegally or through police misconduct, with a few exceptions, cannot be used against a defendant.

The Origins of the Doctrine

This rule stems from the Fourth Amendment, which protects people from unreasonable searches and seizures. However, it dates back only to the early 20th century.

There was a time when law enforcement officers often conducted searches without warrants and used other unscrupulous methods of obtaining evidence. However, a 1914 U.S. Supreme Court case helped change that. The justices overturned the conviction of a man for illegal gambling because the evidence used to convict him was found in a warrantless search of his home. This led eventually to the exclusionary rule and the fruit of the poisonous tree doctrine, which provide the real enforcement of protections outlined in the Fourth Amendment.

Key Exceptions

There are four key exemptions to this doctrine that allow prosecutors to use evidence that was obtained illegally or through misconduct:

* The evidence would have been discovered inevitably anyway.
* The evidence was discovered at least partially by some method that wasn't illegal or inappropriate.
* Law enforcement officers were acting in good faith even without a valid warrant.
* The link between the illegally-obtained evidence and the crime is weak (attenuated).

People may be arrested because of tainted evidence without even realizing it. For example, if they are denied an attorney and then give a confession to officers due to pressure or sheer exhaustion, that confession may be considered tainted. The same is true if a person denies officers the right to search his or her vehicle and they do anyway, discovering something illegal.

Of course, there are situations where the question of whether this doctrine applies may be murky. In these cases, prosecutors will likely fight to allow the evidence in -- particularly if it's important to their case. Experienced criminal defense attorneys can work to help prevent that from happening and ensure that their client isn't convicted of a crime by "fruit of the poisonous tree."