What's Causation Got to Do With It? Suppressing Fruit of the Poisonous Tree
by Sherry F. Colb
In my Verdict column for this week, I discuss Utah v. Strieff, a Fourth Amendment case about the reach of the exclusionary rule. In Strieff, a police officer admittedly violated the Fourth Amendment when he stopped a pedestrian without reasonable suspicion. After asking for identification, the officer called dispatch and learned that there was an outstanding arrest warrant for the man he had illegally stopped. The officer went on to arrest the man and search him incident to that arrest (an ordinarily valid move), and the search turned up evidence of drugs and drug paraphernalia. The issue presented to the Supreme Court is whether the evidence should have been ruled inadmissible fruit of the poisonous tree, the unreasonable stop.
In my column, I discuss the different ways in which the Court might think about the case, depending upon whether it wishes to continue its increasingly hostile stance toward exclusion or whether it prefers to utilize exclusion in cases in which the evidence at issue is plainly available only because of an earlier unreasonable stop. In this post, I want to consider a different question: why should the causal link between the Fourth Amendment violation and the discovered evidence matter so much?
In the fruit of the poisonous tree doctrine, as discussed at length in Wong Sun v. United States, the Court clarified that when determining whether to suppress evidence as the "fruit" of a Fourth Amendment violation, it is necessary to make a determination of whether absent the violation, the evidence would still have been found and, if not, whether the link between the violation and the evidence might still be sufficiently attenuated (by time, the free will of the suspect, or intervening circumstances) that it is nonetheless fair to say that the "taint" of the violation has been dissipated and the evidence ought to come in.
The causal analysis we see here resembles what we find in tort law and criminal law, when we are trying to determine causal responsibility. In these areas, even though the mother of a defendant literally "caused" the defendant's crime or tort in the "but for causation" sense (absent her giving birth to him, the crime or tort would not have taken place), the "taint" of her having birthed him is sufficiently attenuated by time and her son's own independent choices that we certainly will not hold her causally accountable for his actions.
In torts and criminal law, part of what we are doing in assessing causation is determining whether the tortfeasor's or criminal's actions logically encompass the bad outcomes of those actions such that the tortfeasor or criminal should be held accountable and punished for those outcomes. In the Fourth Amendment, however, the Supreme Court has long held that the exclusionary rule is not about giving the police the punishment they deserve and that utilizing the evidence turned up is not itself a violation of the Fourth Amendment (in the way that, say, keeping and using property that one has stolen might further extend the original theft). The exclusionary rule, according to the Court, has little to do with the Fourth Amendment itself but instead serves--in some cases--as a means of deterring violations. Given this approach, it would seem that causation should perhaps play a less significant role than it does in calculating whether to apply the exclusionary rule in a given case.
Consider why this is so. If a police officer violates the Fourth Amendment by stopping a pedestrian without reasonable suspicion, the Court regards the entirety of the Fourth Amendment violation to have already taken place once the stop has happened (or at the point when the stop turns into a lawful arrest on the outstanding warrant that has been discovered). Exclusion is not about punishing the officer with what he deserves (i.e., maybe he "deserves" never to have located the outstanding arrest warrant that ultimately led to the evidence found on the suspect's person, because the discovery only happened as a result of the officer's wrongdoing), and it is not about refusing to admit tainted evidence (tainted by its causal link to the Fourth Amendment violation) in court, due to what some have understood to be a Fourth Amendment obligation on the part of the court not to consider unreasonably obtained evidence (sometimes known as the "judicial integrity" argument for exclusion). The sole objective of exclusion, by the Court's decades-old precedents, is to deter the officer and other officers from violating the Fourth Amendment again.
If one's goal is to deter future stops without reasonable suspicion, then it would seem wise to find that even if there is a possibility that the unreasonable stop led up to the evidence located on the suspect, the evidence should be suppressed. That is, if a police officer knows that no usable evidence can come of an unreasonable stop, then the officer will likely decide to skip the stop altogether, because what is the point? On the other hand, if usable evidence might emerge from the unreasonable stop, then there is little downside to the officer's stopping the suspect without reasonable suspicion. The worst thing that happens is that there is no evidence (or that a court finds the evidence too closely linked to the violation), so the officer has wasted her time. But there is a strong potential upside as well: a court might find that the officer would have found the evidence anyway or that the taint has been dissipated by the passage of time or by intervening acts of free will or other events (such as the existence of the outstanding arrest warrant). As I have said elsewhere, a "perhaps this will be excluded" approach to Fourth Amendment violations functions as no more of a deterrent than a "shoplifters may have to return the property they stole" approach to theft. Without punishment, it is necessary, to accomplish deterrence, at the very least to suppress anything that might have been the fruit of a violation.
This point about deterrence and causation may not be new, but it is worth repeating here, because a (somewhat lukewarm) commitment to deterrence appears to be all that is left of the Fourth Amendment exclusionary rule, a rule that used to be thought a necessary corollary of the Fourth Amendment itself. If one is truly after deterrence, then one does not ask "is it possible that the reward to the officer would have come about even absent the violation?" One asks instead whether admitting this evidence might lead the next officer (or this officer himself) to carry out an illegal stop again in the future. Since the answer to this question will plainly be yes whenever an officer cares about obtaining usable evidence (which is presumably virtually always), a true dedication to deterrence would skip the intricate causation analysis and simply suppress the evidence. And if the officer believes, "Hey, I could have gotten that same evidence without violating the Fourth Amendment!," then so much the better for deterrence, because that is exactly what we want the police officer to do next time. If there is a lawful path to obtaining the evidence, the plain and unequivocal incentive should be for the officer to select that path every time.
In my Verdict column for this week, I discuss Utah v. Strieff, a Fourth Amendment case about the reach of the exclusionary rule. In Strieff, a police officer admittedly violated the Fourth Amendment when he stopped a pedestrian without reasonable suspicion. After asking for identification, the officer called dispatch and learned that there was an outstanding arrest warrant for the man he had illegally stopped. The officer went on to arrest the man and search him incident to that arrest (an ordinarily valid move), and the search turned up evidence of drugs and drug paraphernalia. The issue presented to the Supreme Court is whether the evidence should have been ruled inadmissible fruit of the poisonous tree, the unreasonable stop.
In my column, I discuss the different ways in which the Court might think about the case, depending upon whether it wishes to continue its increasingly hostile stance toward exclusion or whether it prefers to utilize exclusion in cases in which the evidence at issue is plainly available only because of an earlier unreasonable stop. In this post, I want to consider a different question: why should the causal link between the Fourth Amendment violation and the discovered evidence matter so much?
In the fruit of the poisonous tree doctrine, as discussed at length in Wong Sun v. United States, the Court clarified that when determining whether to suppress evidence as the "fruit" of a Fourth Amendment violation, it is necessary to make a determination of whether absent the violation, the evidence would still have been found and, if not, whether the link between the violation and the evidence might still be sufficiently attenuated (by time, the free will of the suspect, or intervening circumstances) that it is nonetheless fair to say that the "taint" of the violation has been dissipated and the evidence ought to come in.
The causal analysis we see here resembles what we find in tort law and criminal law, when we are trying to determine causal responsibility. In these areas, even though the mother of a defendant literally "caused" the defendant's crime or tort in the "but for causation" sense (absent her giving birth to him, the crime or tort would not have taken place), the "taint" of her having birthed him is sufficiently attenuated by time and her son's own independent choices that we certainly will not hold her causally accountable for his actions.
In torts and criminal law, part of what we are doing in assessing causation is determining whether the tortfeasor's or criminal's actions logically encompass the bad outcomes of those actions such that the tortfeasor or criminal should be held accountable and punished for those outcomes. In the Fourth Amendment, however, the Supreme Court has long held that the exclusionary rule is not about giving the police the punishment they deserve and that utilizing the evidence turned up is not itself a violation of the Fourth Amendment (in the way that, say, keeping and using property that one has stolen might further extend the original theft). The exclusionary rule, according to the Court, has little to do with the Fourth Amendment itself but instead serves--in some cases--as a means of deterring violations. Given this approach, it would seem that causation should perhaps play a less significant role than it does in calculating whether to apply the exclusionary rule in a given case.
Consider why this is so. If a police officer violates the Fourth Amendment by stopping a pedestrian without reasonable suspicion, the Court regards the entirety of the Fourth Amendment violation to have already taken place once the stop has happened (or at the point when the stop turns into a lawful arrest on the outstanding warrant that has been discovered). Exclusion is not about punishing the officer with what he deserves (i.e., maybe he "deserves" never to have located the outstanding arrest warrant that ultimately led to the evidence found on the suspect's person, because the discovery only happened as a result of the officer's wrongdoing), and it is not about refusing to admit tainted evidence (tainted by its causal link to the Fourth Amendment violation) in court, due to what some have understood to be a Fourth Amendment obligation on the part of the court not to consider unreasonably obtained evidence (sometimes known as the "judicial integrity" argument for exclusion). The sole objective of exclusion, by the Court's decades-old precedents, is to deter the officer and other officers from violating the Fourth Amendment again.
If one's goal is to deter future stops without reasonable suspicion, then it would seem wise to find that even if there is a possibility that the unreasonable stop led up to the evidence located on the suspect, the evidence should be suppressed. That is, if a police officer knows that no usable evidence can come of an unreasonable stop, then the officer will likely decide to skip the stop altogether, because what is the point? On the other hand, if usable evidence might emerge from the unreasonable stop, then there is little downside to the officer's stopping the suspect without reasonable suspicion. The worst thing that happens is that there is no evidence (or that a court finds the evidence too closely linked to the violation), so the officer has wasted her time. But there is a strong potential upside as well: a court might find that the officer would have found the evidence anyway or that the taint has been dissipated by the passage of time or by intervening acts of free will or other events (such as the existence of the outstanding arrest warrant). As I have said elsewhere, a "perhaps this will be excluded" approach to Fourth Amendment violations functions as no more of a deterrent than a "shoplifters may have to return the property they stole" approach to theft. Without punishment, it is necessary, to accomplish deterrence, at the very least to suppress anything that might have been the fruit of a violation.
This point about deterrence and causation may not be new, but it is worth repeating here, because a (somewhat lukewarm) commitment to deterrence appears to be all that is left of the Fourth Amendment exclusionary rule, a rule that used to be thought a necessary corollary of the Fourth Amendment itself. If one is truly after deterrence, then one does not ask "is it possible that the reward to the officer would have come about even absent the violation?" One asks instead whether admitting this evidence might lead the next officer (or this officer himself) to carry out an illegal stop again in the future. Since the answer to this question will plainly be yes whenever an officer cares about obtaining usable evidence (which is presumably virtually always), a true dedication to deterrence would skip the intricate causation analysis and simply suppress the evidence. And if the officer believes, "Hey, I could have gotten that same evidence without violating the Fourth Amendment!," then so much the better for deterrence, because that is exactly what we want the police officer to do next time. If there is a lawful path to obtaining the evidence, the plain and unequivocal incentive should be for the officer to select that path every time.