What is the 'fruit of the poisonous tree' doctrine?

If police obtained evidence by violating a person's Fourth Amendment rights (such as by performing an illegal search and seizure), it is possible that the evidence will be deemed off-limits for use in a criminal prosecution. This is due to the exclusionary rule, which we discussed in a post a couple months back.

However, an unconstitutional action by police can render more evidence inadmissible than just the evidence directly acquired by it. This is due to another legal rule, which will be the topic of our discussion today. This rule is called the "fruit of the poisonous tree" doctrine.

This doctrine expands the evidence that can be made inadmissible by an unconstitutional police action to include any evidence that was uncovered by police actions that came about as the result of the unconstitutional action. For example, if an illegal search or evidence directly acquired through an illegal search led police to conduct another search, evidence found in that subsequent search could potentially be thrown out under the "fruit of the poisonous tree" doctrine.

Thus, under this doctrine, if an unconstitutional police action led to a bunch of other actions by police, the unconstitutionality of the initial action could bring into question the admissibility of a whole constellation of evidence.

Thus, when mounting a defense in a drug case, it can be remarkably important to carefully look at whether police committed any unconstitutional actions. As one can see, the exclusionary rule and the "fruit of the poisonous tree" doctrine make it so evidentiary matters in a criminal case can be greatly affected if there is a finding that police acted unconstitutionally in the case.

Source: FindLaw, "The Fourth Amendment and the 'Exclusionary Rule'," Accessed Feb. 6, 2015

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