The exclusionary rule and its exceptions

Prosecutor Margaret Liu returns for Lesson 11 with a single page from a judgment. It describes a traffic stop in which an officer, with no real grounds, searched a car and found a large quantity of drugs. The judge found the search unlawful but had to decide whether to admit the drugs anyway. Liu asks the class to vote before reading the ending. Most vote to admit: the drugs are real, the driver is guilty, and excluding them seems like letting the officer's mistake free a criminal. Liu then reads the judge's reasons for excluding them. The conversation that follows is the core of this lesson: why American courts exclude evidence obtained unconstitutionally, and the many exceptions that limit the rule.

The purpose of the exclusionary rule

The exclusionary rule says that evidence obtained in violation of the Fourth Amendment, and statements obtained in violation of the Fifth Amendment or Miranda, cannot be used in the prosecution's case against the defendant. The federal rule began with Weeks v. United States in 1914, and Mapp v. Ohio applied it to the states in 1961. The modern Supreme Court has described the rule's sole purpose as deterring future police misconduct, not remedying the violation for the individual defendant. Because of that, the Court asks whether the benefits of deterrence outweigh the heavy costs of letting guilty people go free, and it has created exceptions where it thinks exclusion would not deter.

Marco DiSanto asks why society should accept losing reliable evidence at all. Liu answers that both systems are responding to the same problem: without some consequence, constitutional rights become advice that officers can ignore whenever they think the result will be worth it. American courts frame the consequence in terms of deterrence, on the theory that officers and agencies follow the rules more carefully when violations cost them cases. Either way, the remedy exists because rights without remedies are not rights at all.

The fruit of the poisonous tree

Exclusion reaches beyond the evidence directly obtained in the violation. In Wong Sun v. United States in 1963, the Court held that evidence derived from an illegal search or arrest, such as a statement made after an unlawful entry or items found by following up on it, is also excluded as fruit of the poisonous tree, unless the connection has become so attenuated that the taint is dissipated. Derivative evidence from a Miranda violation is treated differently: physical evidence found because of a voluntary but unwarned statement is generally admissible, as United States v. Patane held in 2004.

The exceptions

The Court has recognized several exceptions. The good faith exception, from United States v. Leon in 1984, admits evidence obtained by officers who reasonably relied on a warrant that later proved invalid; later cases extended it to reliance on statutes later struck down, Illinois v. Krull in 1987, to negligent database errors, Herring v. United States in 2009, and to binding appellate precedent later overruled, Davis v. United States in 2011. The independent source doctrine admits evidence also obtained through a lawful source unconnected to the violation, Murray v. United States in 1988. The inevitable discovery doctrine admits evidence that would certainly have been found lawfully, Nix v. Williams in 1984. The attenuation doctrine admits evidence when the connection to the violation is too remote, considering time, intervening circumstances and the flagrancy of the misconduct, Brown v. Illinois in 1975; in Utah v. Strieff in 2016, the discovery of an outstanding arrest warrant during an unlawful stop was held to break the chain.

Two more rules limit exclusion. Standing: only a person whose own rights were violated can seek suppression; a passenger usually cannot challenge the search of a car they do not own or control, Rakas v. Illinois held in 1978, although an unauthorized driver of a rental car can, Byrd v. United States held in 2018. Impeachment: unconstitutionally obtained evidence, including statements taken in violation of Miranda if voluntary, can be used to impeach a defendant who testifies inconsistently, as Harris v. New York held in 1971. And in Hudson v. Michigan in 2006, the Court held that a violation of the knock-and-announce rule does not require suppression.

What makes conduct serious

Liu walks the class through the kinds of police conduct that make exclusion most likely. Deliberate shortcuts, such as searching first and finding grounds later, are the most serious. Ignorance of well-established rules, such as not knowing that a phone search needs a warrant, comes next, because courts expect officers to know clearly established law. A pattern of similar breaches, whether by one officer or across a service, makes each breach worse. And misleading testimony about what happened is especially damaging, because it attacks the court's ability to find the truth. On the other side, careful documentation, a genuine effort to comply, prompt correction of errors and candour in court all reduce seriousness, even when a mistake was made.

Desjardins adds that the attitude of the officer on the stand often decides how a judge sees the whole investigation. An officer who says, 'I made a mistake about the timing of the rights advice, here is what happened and why,' is believed on everything else. An officer who insists that nothing went wrong when the video shows otherwise can lose the evidence and their credibility in one afternoon. Courts have repeatedly found that officers' false testimony aggravates violations, and it can expose officers to prosecution and decertification.

Port Ardent applications to exclude

Liu has tracked every application to suppress evidence in Port Ardent cases over three years, by the main issue raised. The program summarizes how often each kind of application succeeded.

# Port Ardent applications to exclude or suppress evidence over three years, by main issue
applications = {
    "search without grounds": (31, 14),
    "phone search": (9, 6),
    "right to counsel": (27, 12),
    "detention": (18, 5),
    "statement voluntariness": (12, 4),
}
total_apps = sum(a for a, _ in applications.values())
total_granted = sum(g for _, g in applications.values())
print("applications:", total_apps, "granted:", total_granted, "rate:", round(total_granted / total_apps, 2))
for issue, (apps, granted) in sorted(applications.items(), key=lambda kv: -kv[1][1] / kv[1][0]):
    print(f"{issue:24s} {granted:2d} of {apps:2d}  {granted / apps:.2f}")

applications: 97 granted: 41 rate: 0.42
phone search              6 of  9  0.67
search without grounds   14 of 31  0.45
right to counsel         12 of 27  0.44
statement voluntariness   4 of 12  0.33
detention                 5 of 18  0.28

About four applications in ten succeeded. Phone searches had the highest success rate, two in three, because the rule is clear and officers who search without a warrant have little excuse. Searches without grounds and right to counsel issues produced the largest numbers of exclusions. Liu tells the class that almost every one of those cases began with a step that an officer could have done differently in seconds: waiting for a warrant, writing down the grounds, or holding off on a question.

How an application to exclude unfolds

Students often imagine exclusion as a dramatic moment in the middle of a trial. In practice it is a structured process. The defense files a motion to suppress before trial, setting out the alleged violation and the evidence to be excluded. The court holds a suppression hearing, often well before trial, where officers testify and are cross-examined about the grounds, the timing and what they did. The judge decides whether there was a violation, whether the defendant has standing, whether the evidence is fruit of the violation and whether an exception applies. A ruling suppressing key evidence often ends the case through dismissal or a plea.

For officers, the hearing is where the quality of their notes and reports matters most. The judge will compare the officer's testimony with the notes, the report, the dispatch records and any video, minute by minute. Inconsistencies that seem trivial, such as a time that differs by a few minutes or a detail added in the report that is not in the notes, can lead a judge to doubt the officer's whole account. Desjardins tells the class that the best preparation for a suppression hearing begins on the night of the arrest, with notes that are complete, specific and written at the time.

Exclusion and civil liability are separate questions

An officer's conduct can be judged in more than one forum, and the outcomes do not always match. Evidence may be admitted under an exception even though a violation occurred, and the person may still sue under 42 U.S.C. 1983 if the violation was clearly established, or file a complaint that leads to discipline. Equally, evidence may be suppressed while the officer is protected from civil damages by qualified immunity. Marco asks which consequence officers should worry about most. Desjardins says the question misses the point: officers who follow the rules carefully rarely face any of them, and the habits that protect evidence are the same ones that protect officers from complaints and lawsuits.

Desjardins closes the section with a reminder about candour. When an officer realizes that a mistake was made, the right response is to tell the prosecutor at once, so that the prosecution can decide how to handle it and disclose it properly. Prosecutors can often work around a disclosed mistake. What they cannot work around is a mistake that surfaces for the first time during cross-examination, because by then the issue is no longer only the mistake but the officer's honesty about it.

Liu finishes with a piece of advice from her own experience. When she prepares officers for a hearing, she asks them to walk her through the night in their own words before they look at their notes, then compares the account with the notes. The gaps tell her where an officer's memory has filled in details since the night, which is natural and human but dangerous on the stand. Officers who know the difference between what they remember and what they wrote can say so clearly in court, and judges trust them for it. Officers who blur the two often find that a single confident detail, contradicted by the video, undoes an otherwise lawful investigation.