What Happens When A Search Violates the Fourth Amendment

If, upon review, a court finds that an unreasonable search occurred, any evidence seized as a result of the search cannot be used as direct evidence against the defendant in a criminal prosecution, state or federal. This rule, established by the U.S. Supreme Court in 1961, has come to be known as the "exclusionary rule." To this day, many commentators criticize it 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 won't conduct improper searches if the resulting evidence can't be used to convict the defendant.

In addition to being excluded as evidence against the defendant, evidence resulting from an illegal search may not be used to discover other evidence, under a legal rule 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 inadmissible at trial.

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 be:

• considered by a judge when deciding on an appropriate sentence following conviction
• admitted in civil cases and deportation cases, and
• in some circumstances, be used by a prosecutor to impeach (attack the credibility of) a witness who testifies in the trial.