The Probable Cause Standard

The Probable Cause Standard

Once police conduct has become an arrest, the Fourth Amendment asks whether the officers had probable cause to make it. In Beck v. Ohio the Court framed the question as whether, at the moment the arrest was made, the facts and circumstances within the officers' knowledge, and of which they had reasonably trustworthy information, were sufficient to warrant a prudent person in believing that the suspect had committed or was committing an offense.¹ That formulation holds three separate demands, one about timing, one about the quality of the officer's information, and one about how much belief is enough, and the first sub-section below takes them apart. The reasons for the standard come first, because each of its features answers a specific risk in the way arrests happen.

The amount of belief the standard demands is a compromise between two opposing interests. The Court has called probable cause a practical, nontechnical conception that gives the best available accommodation of those interests: requiring more would "unduly hamper law enforcement," while allowing less would leave law-abiding citizens "at the mercy of the officers' whim or caprice."² Each side of the compromise has a concrete mechanism behind it. An arrest opens the inquiry into guilt rather than closing it, so an officer who needed proof sufficient to convict before taking a suspect into custody could seldom act while the suspect was still there to be arrested. A hunch-level threshold fails from the other direction, because the officer's own impulse would then be all that stood between a person and custody. Between those poles the standard asks for a belief that a prudent person would share, built on facts.

The timing feature matters most in the situation Beck itself presented, an arrest made without a warrant. A warrant puts the probable cause question to a neutral magistrate before anyone is taken into custody, on facts presented in advance. A warrantless arrest skips that step, so the first neutral review comes afterward, in a suppression hearing, when everyone in the courtroom already knows how the arrest turned out. The Court described that after-the-event justification as "too likely to be subtly influenced by the familiar shortcomings of hindsight judgment."³ Fixing attention on what the officers knew at the moment they acted is the safeguard against that distortion, because it forces the reviewing court to set aside whatever the arrest, or the search that followed, happened to turn up. Beck also endorses the observation that the demands of reliability and particularity for a warrantless arrest cannot be lower than for an arrest under a warrant, since otherwise officers would gain by skipping the magistrate and a principal reason for obtaining warrants would disappear.⁴

The standard is also measured by facts rather than by the officer's sincerity. In Beck the Court assumed that the officers acted in good faith and still found the arrest invalid, explaining that if subjective good faith alone were the test, the Fourth Amendment's protections would evaporate and people would be secure only in the discretion of the police.⁵ A belief the officer holds sincerely but cannot trace to specific, trustworthy facts gives a reviewing court nothing to evaluate, which is why the test looks to the facts the officer had, and the officer's confidence adds nothing to them. With those reasons in place, the two sub-sections below state the test and then show a record that failed it.

The Probable Cause Test

The three demands in Beck combine into a single rule: probable cause to arrest exists when, at the time of arrest, the officer has reasonably trustworthy facts and circumstances within the officer's knowledge sufficient to warrant a reasonably prudent person in believing that the suspect has committed or is committing a crime for which arrest is authorized by law.⁶ Each phrase does its own work. The words "at the time of arrest" fix the clock. The requirement that the facts be within the officer's knowledge, and reasonably trustworthy, sets the quality of the raw material: what counts is what the officer actually knew, whether seen firsthand or relayed by someone else, and relayed information counts only if there is reason to credit it. The reasonably prudent person supplies the yardstick for how much those facts must add up to, and the object of the belief is specific, namely that the suspect committed or is committing a crime for which the law authorizes arrest, so a prudent sense that someone is behaving oddly does not meet it.

The second step is where arrests most often fail, and the error students most often make is to count what the search later turned up toward probable cause. In Beck the officers stopped the driver, arrested him, searched his car and found nothing, then took him to the station and found clearing house slips beneath his sock.⁷ The slips were the only physical evidence of a crime in the case, yet they could not justify the arrest that produced them. The search was defended as incident to a lawful arrest, so its validity depended on the arrest, and the arrest depended on what the officers knew when they made it.⁸

On the question of how much belief suffices, the standard sits well below the proof needed at trial. In Maryland v. Pringle the Court recalled that probable cause means less than evidence that would justify condemnation, and that finely tuned standards such as proof beyond a reasonable doubt or a preponderance of the evidence have no place in the decision.⁹ The reviewing court examines the events leading up to the arrest and asks whether those historical facts, viewed from the standpoint of an objectively reasonable police officer, amount to probable cause.¹⁰ Falling below the trial standard still leaves a floor, because the facts must be specific and trustworthy enough that a prudent person would form the belief, and that floor is where the arrest in Beck gave way.

Bare Conclusions Fall Short

The record in Beck shows what it looks like when the facts fall beneath that floor. The State's entire showing was the testimony of one arresting officer at the suppression hearing.¹² The officer knew Beck's appearance from a police picture and knew that Beck had a record in connection with clearing house offenses, and beyond that testified only that he had "information" and had "heard reports" from someone he could identify but did not describe.¹³ Nothing in the record revealed what the information was or where it came from, nothing suggested that any informer had said Beck could be found at that corner at that time, and the officers did not see Beck stop or perceive anything else suggesting that he was acting unlawfully.¹⁴ The Court observed that no decision of its own had upheld a warrantless arrest on support so scant, and it reversed the conviction.¹⁵

Two gaps in that record deserve separate attention. The first is the reliance on appearance and criminal record. The Court did not call the officer's knowledge of those facts irrelevant, but it held that treating either or both as probable cause would mean that anyone with a previous record could be "arrested at will."¹⁶ A record describes a person's past and a whole class of former offenders, and it says nothing about whether this person is engaged in this offense now. The second gap is the unexplained "information." The Court acknowledged that an informer may well have told the officer something amounting to probable cause, but once the arrest was challenged the prosecution had to show with considerably more specificity what the informer actually said and why the officer thought it credible.¹⁷ The reason is structural. Probable cause is a judgment the court must make for itself, and a court that is not told the underlying facts cannot make it, so an officer who reports only a conclusion is asking the judge to adopt the officer's own judgment, which is the discretion the standard exists to check.¹⁸

The State relied on Draper v. United States, and the contrast shows what the missing record would have contained. In Draper a named informant who had given reliable information on numerous occasions told the arresting officer that the defendant, whom he described minutely, had taken up residence at a stated address and was selling narcotics, and that the defendant would return from Chicago with narcotics on one of two trains, which he in fact did.¹⁹ What distinguishes the two cases is the content of the record. In Draper the informant's track record showed why the tip deserved belief, the detailed prediction showed how the informant knew, and the officer's own observation at the station confirmed the details before the arrest. In Beck the record held no objective fact of any of those kinds. Corroboration of that sort is how police ordinarily convert a tip into probable cause, since an informant's detailed description of an event that officers then see unfold gives the tip weight it would not otherwise have.²⁰

On an exam stem, a Beck problem announces itself through an officer who testifies in conclusions: "I had information," "I knew his record," "I recognized him." The analysis asks what the information was, who supplied it, and why the officer had reason to believe it, and where the stem supplies no answer, probable cause is missing. Students lose this issue by treating the officer's good faith as a substitute for facts, when the Court assumed good faith in Beck and held that good faith on the part of the arresting officers is not enough.²¹

The Probable Cause Test

The test in Beck v. Ohio compresses into a single rule, and the rule is easiest to apply once its parts are separated. Probable cause to arrest exists when, at the time of arrest, the officer has reasonably trustworthy facts and circumstances within the officer's knowledge sufficient to warrant a reasonably prudent person in believing that the suspect has committed or is committing a crime for which arrest is authorized by law.²³ Four working parts can be pulled out of that sentence. The clock is the moment of arrest, the raw material is what the officer actually knew, the quality control is reasonable trustworthiness, and the yardstick is the belief a prudent person would form from facts of that quality. The preceding discussion explained why the clock and the officer's good faith are fixed as they are, so what follows concerns how the remaining parts operate on a record.

Reasonable trustworthiness matters most when an arrest rests on what other people told the officer, which is how many arrests come about. Officers seldom watch a crime happen; they act on victim reports, dispatches, and informants. The test lets them use that information even when it would be hearsay (an out-of-court statement offered to prove what it asserts) and would be excluded at trial, because the trial rules of evidence exist partly to keep jurors from misusing information, and an officer deciding on the street is not a juror.²⁴ What the test asks of such information is reliability. A tip counts for as much as there is reason to credit it, and that reason has to exist when the officer acts. A source with a record of accurate information, a tip rich in detail that the officer can check, and a report from a victim who saw the events firsthand all carry weight, while an unexplained claim that the officer has information carries none.²⁵

Beck itself marks the line by comparing its own record with Draper v. United States. In Draper a named informant who had given reliable information on numerous occasions described the suspect in detail, said where he lived and that he sold narcotics, and predicted that he would return from Chicago with narcotics on one of two trains; the suspect arrived as predicted, and the arrest on probable cause was upheld.²⁶ Each feature answered a question about the tip. The track record showed why the source deserved belief, the detailed prediction showed how the source could know, and the suspect's arrival confirmed the prediction. Beck's officer could offer none of that. He knew the driver's appearance from a police photograph and knew of a record involving clearing house offenses, and he added only that he had information and had heard reports from someone he did not describe, which left a prudent person unable to tell whether the driver was committing an offense at that moment.²⁷

Once the facts are filtered, the remaining question is what a reasonably prudent person would believe from them, and that yardstick is objective. The reviewing court examines the events leading up to the arrest and asks whether those historical facts, viewed from the standpoint of an objectively reasonable police officer, amount to probable cause.²⁸ The officer's state of mind therefore drops out in both directions: sincere certainty cannot rescue a thin record, and the absence of subjective belief does not defeat a record that is objectively sufficient.²⁹ The measure is also practical, so an officer's training and experience count, and a trained officer may see significance in facts, such as the smell of an illegal substance, that would mean nothing to a layperson.³⁰ An objective measure is also the workable one, since a court cannot reliably reconstruct what an officer privately felt but can examine what the officer knew.³¹

The belief has a specific object, and the object has two parts. For an arrest there must be probable cause that a crime has been committed and also that the person to be arrested committed it.³² A search asks a different pair of questions, whether the items sought are connected with crime and whether they will be found in the place to be searched, and it can succeed without implicating any particular person.³³ An arrest takes a person into custody, so the belief must be particularized to that person, and standing near criminal activity does not carry the belief by itself.³⁴ The crime must also be one for which arrest is authorized by law, which excludes conduct that is merely odd without being criminal. The offense need not be serious, since probable cause to believe someone committed even a very minor offense in the officer's presence permits an arrest, a point taken up later in this chapter.³⁵

A victim's excited statement identifying a man as the person who broke into her car and took money from her purse shows both parts at once. It reports a crime and points to a person, and the arrest is justified because the officer reasonably believes it, whether or not the man later proves to be the thief.³⁶

How much belief is enough? Far less than proof. Probable cause means less than evidence sufficient to condemn, and the finely tuned standards used at trial, such as proof beyond a reasonable doubt or a preponderance of the evidence, have no place in the decision.³⁷ The standard resists conversion into a percentage because it deals in probabilities and depends on the totality of the circumstances.³⁸ Yet the floor sits above a hunch: an arrest must rest on firmer ground than mere suspicion, even though the officer need not hold evidence that would suffice to convict.³⁹ The band between those limits exists because ambiguity is the ordinary condition of police work. Room must be left for mistakes, provided they are the mistakes of reasonable people acting on facts that lead sensibly to their conclusions, which means an arrest can be valid even though the person arrested turns out to be innocent.⁴⁰ And because the same standard governs every arrest without case-by-case balancing, a restraint that amounts to an arrest cannot be justified by pointing to some lesser level of suspicion.⁴¹

The second step is where arrests most often fail, and Beck shows the mechanics. The officers stopped the driver, arrested him, searched his car and found nothing, and found the clearing house slips only at the station, beneath his sock.⁴² The slips were the only physical evidence of crime in the case, but they surfaced after the arrest and so could not supply the probable cause the arrest needed when it was made. The search was defended as incident to a lawful arrest, which tied its validity to the arrest, and the arrest depended on what the officers knew at the moment they acted.⁴³

Three errors recur on exam stems. Students count what the search later turned up, which the moment-of-arrest rule forbids. They reject a tip because it would be inadmissible at trial, which imports a trial rule into a decision governed by reliability. And they demand more than the standard asks, whether proof that the suspect actually committed the offense or a showing of fifty percent likelihood, when neither is required.⁴⁴

Bare Conclusions Fall Short

The probable cause test is applied to a record, and a court can credit only the facts that the record contains. Beck v. Ohio is the standard illustration of a record that held almost none. The only evidence of what the arresting officers knew was the testimony of one of them at the suppression hearing, and it came to three items: the officer had seen a police photograph of the suspect and knew what he looked like, knew that he had a record in connection with clearing house and scheme-of-chance offenses, and had "heard reports" from someone the officer said he could name but did not.⁴⁶ The testimony never disclosed what the reports said or where they came from, and it did not suggest that any informant had said the suspect could be found at that place and time. Nor did it show that the officers saw, heard, or smelled anything indicating that the suspect was breaking the law.⁴⁷ The Court held that this record could not support the arrest, and its reasons divide into three parts.

The first part concerns what appearance and a prior record can prove. The Court did not call the officer's knowledge of the suspect's looks and history inadmissible or irrelevant, but it refused to treat either fact, or both together, as probable cause, because that would mean that anyone with a previous criminal record could be arrested at will.⁴⁸ A record is a permanent fact about a person. It was as true the year before the arrest as on the night of it, so it says nothing about whether the person is committing an offense now, and a rule that let it carry an arrest would leave every former offender open to seizure whenever an officer chose. Reputation fares no better. In Spinelli v. United States the Court described a general assertion that the defendant was known as a gambler as "a bald and unilluminating assertion of suspicion that is entitled to no weight."⁴⁹ The concrete facts that give rise to a bad reputation may be weighed, because probable cause must be shown through facts rather than conclusions, but the reputation as a label contributes nothing.⁵⁰

The second part concerns the unnamed source, and it is partly a rule about proof. When an arrest is challenged, the court must decide whether the facts available to the officers at the moment of arrest would warrant a person of reasonable caution in believing that an offense had been committed, and a court that is not told those facts cannot perform that function.⁵¹ The Beck officer told the court only that someone had said something about the suspect. The Court allowed that an informant may in fact have supplied information amounting to probable cause, but held that the prosecution had to show with considerably more specificity what the informant actually said and why the officer thought the information credible.⁵² The defect therefore has two layers. On substance, a label such as information contains no fact that a prudent person could evaluate. On proof, even if the officer really did hold good information, the State never put it in the record, and an arrest defended only by what the officer might have known is defended by nothing a court can examine. A prosecutor cannot cure that gap by urging that the arrest was probably sound, since the obligation to show the facts fell on the prosecution.

The reason for demanding specifics comes from how a warrantless arrest works. It skips the advance review of a neutral judicial officer and substitutes an after-the-event justification, which the Court regarded as too likely to be shaped by the shortcomings of hindsight.⁵³ That substitution creates an incentive problem. If officers could meet the standard by reciting conclusions, a vague account would be the safest account to give, since it cannot be contradicted, and the court would end up ratifying the officer's own judgment instead of making its own. Wong Sun v. United States applied the same logic to an arrest that rested on an accusation by an informant whose reliability had not been shown: on the sparse information the agents had, no arrest warrant could have issued, so the arrest without one could not stand.⁵⁴ Warrant applications obey the same rule, because a magistrate's action cannot be a mere ratification of the bare conclusions of others.⁵⁵

The third part removes the officer's sincerity from the analysis. The Court assumed that the Beck officers acted in good faith and held that "good faith on the part of the arresting officers is not enough."⁵⁶ If subjective good faith alone were the test, the Fourth Amendment's protections would evaporate, and people would be secure only in the discretion of the police.⁵⁷ The same cases describe the floor from the other direction: an arrest, with or without a warrant, must stand on "firmer ground than mere suspicion," though the officer need not hold evidence sufficient to convict.⁵⁸ Sincere conviction is the one thing a thin record always has, which is why it cannot be the thing that rescues it.

A record with facts in it shows what the missing material would have looked like. The State in Beck relied on Draper v. United States, where a named informant with a record of reliable information had described the suspect minutely and predicted his arrival with narcotics on one of two trains, and the prediction came true. The Court answered that the Beck record contained not a single objective fact of that kind.⁵⁹ A search-warrant case, Andresen v. Maryland, supplies a second contrast. There the affidavits named the complainants, described their positions, related their transactions in comprehensive detail, and reported that agents had checked the accounts against correspondence, documents, and public land records, which led the Court to say it had rarely seen affidavits so complete.⁶⁰ In each, a judge could see who the source was, how the source knew, and what had been verified.

An invalid arrest carries a second consequence beyond the arrest itself. The search of the suspect in Beck was defended only as incident to a lawful arrest, so when the arrest failed for want of probable cause the search failed with it, and the Court reversed the conviction.⁶¹ The authority to search comes from the arrest, so an arrest that was unlawful when made passes on none. What the search later turns up cannot repair the defect: Wong Sun refused to let ambiguous conduct that the officers themselves provoked turn a vague suspicion into probable cause, because that would validate an intrusion by what it produced.⁶² The Court then held inadmissible the statement and the heroin that flowed from the unlawful arrest.⁶³ A dissenting opinion in Chimel v. California, which would have allowed broader searches after an arrest, still treated the arrest's validity as a precondition, reasoning that circumstances created by an unlawful arrest cannot justify the search that accompanies it.⁶⁴

A stem announces this issue when the officer testifies in conclusions: the officer had information, knew the suspect's record, recognized the suspect. Students lose points by treating the existence of an informant as though it were what the informant said, when the record must show the content of the tip and the reason to believe it. A stem that supplies those answers, such as a named source with a track record whose detailed prediction the officer watched come true, reverses the result.