While the justice system is not perfect in this country, it is one of the most fair systems in the world. It affords the accused every opportunity to maintain their innocence. Besides “innocent until proven guilty”, the law recognizes the doctrine of “fruit of the poisonous tree”, a doctrine that extends the exclusionary rule to make evidence inadmissible in court if it was derived from evidence that was illegally obtained. As the metaphor suggests, if the evidential “tree” is tainted, so is its “fruit.” The doctrine was established in 1920 by the decision in Silverthorne Lumber Co. v. United States, and the phrase “fruit of the poisonous tree” was coined by Justice Frankfurter in his 1939 opinion in Nardone v. United States.
Like the exclusionary rule itself, this doctrine is subject to three important exceptions. The evidence will not be excluded:
- if it was discovered from a source independent of the illegal activity;
- its discovery was inevitable;
- or if there is attenuation between the illegal activity and the discovery of the evidence.
Further, if the primary evidence was illegally obtained, but admissible under the good faith exception, its derivatives (or “fruit”) may also be admissible.
The exclusionary rule prevents the government from using most evidence gathered in violation of the United States Constitution. In practice, this requires law enforcement to take care how they question witnesses and suspects as well as how they gather evidence.
These safeguards are meant to enforce the philosophical principle that the end do not justify the means. In other words, a supposed good outcome (an arrest or conviction) is not justified if it were obtained through illegal or corrupt means.
The United States Supreme Court has decided a number of cases related to this doctrine. In the case of United States v. Rey, one justice stated that for the exclusion of evidence to be ordered, the police misconduct must have been “sufficiently deliberate” that future similar conduct would be deterred due to the exclusion and that such future deterrence would be worth the cost to the justice system.
The doctrine was designed to deter police misconduct that is reckless, deliberate or grossly negligent. However, it can also be used to correct widespread systemic negligence. The doctrine may not prevent all types of evidence from being admitted if it would only cause marginal deterrence.