"...the minimal requirement for a reasonable search" (Chambers v. Maroney 1970)
The Fourth Amendment has two clauses. The first states that people have a right to be protected from unreasonable searches and seizures, and the second states that no warrant shall issue except upon probable cause. The roots of the second (2nd) clause -- the probable cause requirement -- lie in English and American colonial history. Prior to the framing of our Constitution by the founding fathers, the government had virtually unlimited power to believe, right or wrong, that any illegal items they were looking for would be found. In England, this all-purpose power took the form of what were called general warrants; in colonial America, they were called writs of assistance. To protect against the abuses inherent in this kind of power, the Framers added a probable cause requirement.
The probable cause requirement is, in many ways, more important than the reasonableness clause. Not all search and seizures require warrants (e.g., automobile searches, arrest in a public place), but the Supreme Court has interpreted warrantless searches and seizures as unreasonable unless preceded by probable cause. This means that as a general rule, most if not all searches and seizures require probable cause.
The concept of probable cause is an example of the procedural law's attempt to balance, or accommodate, competing interests. On the one hand, it protects from arbitrary intrusions into liberty and privacy, but on the other hand, it gives sufficient leeway to government officials by not being as strong of a standard of proof as beyond a reasonable doubt. More leeway is granted to law enforcement under the standard of reasonable suspicion which is enshrined under Stop and Frisk Law. Further, another rather lenient standard exists -- the standard of reasonableness under all circumstances, which is used in school searches and sweeps. The Supreme Court has indicated that any exceptions to the probable cause requirement will be few in number. The Supreme Court has referred to its interpretation of probable cause as the "accumulated wisdom of precedent and experience."
The precise meaning of "probable cause" is somewhat uncertain. Most academic debates over the years have centered around the differences between "more probable than not" and "substantial possibility". The former involves the elements of certainty and technical knowledge. The latter involves the elements of fairness and common sense. There's more adherents of the latter approach, but how do you define common sense. Supreme Court case law has indicated that rumor, mere suspicion, and even "strong reason to suspect" are not equivalent to probable cause. Over the years, at least three definitions have emerged as the best statements:
Probable cause is where known facts and circumstances, of a reasonably trustworthy nature, are sufficient to justify a man of reasonable caution or prudence in the belief that a crime has been or is being committed. (reasonable man definition; common textbook definition; comes from Draper v. U.S. 1959)
Probable cause is what would lead a person of reasonable caution to believe that something connected with a crime is on the premises of a person or on persons themselves. (sometimes called the nexus definition; nexus is the connection between PC, the person's participation, and elements of criminal activity; determining nexus is the job of a judicial official, and it's almost always required in cases of search warrants, not arrest warrants)
Probable cause is the sum total of layers of information and synthesis of what police have heard, know, or observe as trained officers. (comes from Smith v. U.S. 1949 establishing the experienced police officer standard)
There are of course, other definitions, and it's a fact of life in criminal justice that different judicial officials use different definitions. Judges will always have the last word on probable cause. Police will use whatever judicial official is available, preferred, or the court system may have a rotating duty roster for judges or magistrates to sit for nothing but warrants. The Good Faith Exception to the Exclusionary Rule protects the police to some degree in errors made by magistrates (where an appeals court rules that the magistrate signed off too leniently on probable cause). The Sixth Amendment also requires a person arrested without a warrant be brought before a magistrate without delay. This is called First Appearance, and it involves a judicial affirmation of probable cause. Many jurisdictions also still have something called the Preliminary Hearing, and it involves the determination of whether there are reasonable grounds to believe someone is guilty (not reasonable doubt, but jacked-up probable cause). Modernized court systems combine the First Appearance and Preliminary Hearing into one Probable Cause Hearing (eliminating the redundancy).
There are a few things from other areas of the law that have relevance for the law of probable cause. One of these is the area of privacy. A "search" is in many ways a violation of privacy, a quest for something. Therefore, the Katz definition of privacy (expectation of privacy) prevails and in many ways supplements the particularity requirement (searches cannot be exploratory in hopes of finding something; they must be calculated, looking for something specific). Under Katz, only things a person clearly expects or deems private are protected; anything on display or in a public place is not protected. The area of electronic surveillance is also relevant. States cannot generally give their officers more power than the federal government allows when it comes to technology, but there are loosened restrictions on consent and different definitions of private (e.g., email) under wiretapping law. A "seizure" involves a dispossession of a person's exercise of dominion or control of a thing; the detaining of their body in the case of arrest. The only things that should be seized, as a general rule, are items within Plain View or under the immediate control of a suspect (the Chimel Rule), but in some cases (under conspiracy, racketeering, and asset forfeiture laws), a person can be dispossessed of things faraway and distant (like Swiss Bank Accounts) if the items are instrumentalities or proceeds of the crime. The law of seizure generally recognizes two precedent-setting cases:
Brinegar v. U.S. 338 US 160 (1949) -- (Probable Cause to Arrest) -- provides details on how to determine if a crime has been or is being committed
Carroll v. U.S. 267 US 132 (1925) -- (Probable Cause to Search) -- provides details on the belief that seizable property exists in a particular place or on a particular person.
SOURCES OF PROBABLE CAUSE
The basic thrust of the law in this area is that there are some sources of probable cause that need to be supplemented by other sources, and then, there are some sources that are good enough by themselves. There's no need to adhere to a totality of circumstances test, or checklist format (e.g., 4 out of 10 possible sources equals probable cause). The law makes ample use of precedents set in other areas of procedural and evidence law.
Most of the sources can be categorized into four (4) groups:
Observation -- These are things that the police officer obtains knowledge of via the senses: sight, smell, hearing; but this category would also include the kinds of inferences to be made when the experienced police officer is able to detect a familiar pattern (of criminal activity) that contains a series of suspicious behaviors (e.g., circling the block twice around an armored car unloading at a bank).
Expertise -- These are the kinds of things that a police officer is specially trained at; such things as gang awareness and identification, recognition of burglar tools, the ability to read graffitti and tatoos, and various other techniques in the general direction of knowing when certain gestures, movements, or preparations tend to indicate impending criminal activity.
Circumstantial Evidence -- This is evidence that points the finger away from other suspects or an alibi, and by a process of elimination, the only probable conclusion to be drawn is that the person or things left behind is involved in crime.
Information -- This is a broad category which includes informants, statements by witnesses and victims, and announcements via police bulletins, broadcasts, and at roll call.
One can collapse these categories down to two (2) into direct and indirect:
I. Direct Sources of Probable Cause (Officer sources of knowledge)
FLIGHT -- Attempting to flee, evade or elude, is in evidence law a presumption of guilt. It's not by itself sufficient for probable cause, but it's surely going to result in a chase situation and custodial detention of some sort. The case of Wong Sun v. U.S. (1963) covered suspects who run out the side or back door as sufficient for probable cause, however, and there have been other cases in which suspicious behavior like dropping packages or using phones but not talking have held up.
FURTIVE MOVEMENTS -- "Furtive" means secretive or concealing, and the law requires a totality of circumstances here. The movement cannot possibly be construed as an innocent gesture (looking both ways before crossing the street). Nervousness alone is not sufficient as the law recognizes the right of people to be nervous or fearful around police. The movement cannot also be possibly the sign of a mental condition. There must be something secretive given the time, setting, weather, and audience. It would be best if the furtive movements were identifiable with a particular type of crime.
OBSERVATION OF REAL EVIDENCE -- "Real" evidence is demonstrative evidence (Exhibit A) that speaks for itself. Most of the time, these kinds of things are in plain view (binoculars and cameras are allowed as well as normal extensions of the senses, but you can't use a portable microscope to analyze the grass for fibers, e.g.). Fresh footprints is a good example, and the list includes: imprints, impressions, models, diagrams, sketches, photographs, video, and computer animation.
ADMITTED OWNERSHIP -- This involves, for example, a type of consent in which a person, say, accidentally empties the contents of their purse or pockets, and the police ask them if they own something, and they say "yes", and then the police look inside it and find contraband, they are said to have had probable cause for the search and seizure.
FALSE OR IMPROBABLE ANSWERS -- This is not normally a basis of probable cause alone, but it tends to trigger subsequent police inquiry or action. Examples might include a person being asked who the car belongs to, and they say "my cousin" but they don't know their cousin's name. Or, a girlfriend answers the door and says the apartment is rented under her boyfriend's name, but she doesn't know what kind of car her boyfriend drives.
PRESENCE AT A CRIME SCENE or IN A HIGH-CRIME AREA -- The two of these are actually somewhat different. Police have more powers at crime scenes to commandeer something, but in high-crime areas, this source of probable cause is definitely not sufficient by itself, and would probably be an example of nullification under the void-for-vagueness doctrine applicable to loitering. There are a couple of rules, however. The "joint possession" rule means that everyone in the house is subject to search and seizure if the drugs and/or contraband are in a prominent location. The totality of circumstances test applies in high-crime areas where (a) the neighborhood has to have a notorious reputation; (b) there's a typical sequence of events; (c) there's flight or attempted flight; and (d) furtive movements are present.
ASSOCIATION WITH KNOWN CRIMINALS -- This is not sufficient by itself for probable cause, except with some crimes, like conspiracies, counterfeiting, food stamp fraud, etc., where it's probable that others are involved or benefitting from the criminal activity. Association with a known drug dealer can also be incriminating in some cases. The most common case would involve somebody acting as security or a lookout for another, and this would be part of the experienced police officer standard.
PAST CRIMINAL CONDUCT -- An officer's personal knowledge of a suspect's past would be considered more likely to establish probable cause than just knowing they had a rap sheet. The officer would most likely have to know fairly intimate details of the person's life (perhaps by having previously arrested or interrogated them). In most cases, however, knowledge of this information is considered by the law to be relevant, but not sufficient.
FAILURE TO PROTEST -- This is, again, a presumption. Innocent people would react more strongly to various police actions that are incriminating. It definitely cannot be used alone as a basis of probable cause, but the interesting thing about it is that the police have it both ways. A person who is acting extremely submissive or extra "nice" might also be someone who has something to hide.
II. Indirect Sources of Probable Cause (Hearsay Evidence)
Hearsay is any second-hand information. The most common situation involves informants. The history of Informant Law has evolved from:
Aguilar test (1964) -- A two-prong test requiring the affidavit spell out the underlying circumstances of how the informant gained their knowledge AND a statement of the informant's veracity, or record of truthfulness.
Spinelli test (1969) -- A three-prong test requiring all the elements of Aguilar plus an assessment of how accurate the information from the informant might be from a police perspective. Is it against the informant's best interests, for example, to tell the police?
Gates test (1983) -- This replaces both Aguilar-Spinelli tests with a totality of circumstances test, requiring the police to think both like an offender as well as a reasonable man (subjective and objective test). The totality of circumstances test is discussed under the Stop & Frisk lecture, so it's a much looser standard associated more with reasonable suspicion than probable cause.
About.com Guide to Civil Liberties: Search & Seizure
CourtTV Transcripts on Search & Seizure
Legal Updates from the North Carolina Justice Academy
National Association of Criminal Defense Attorneys
Nolo Press Guide on How to Tell if an Arrest is Legal
Klockars, C. (1991). "Getting Around the Fourth Amendment." in C. Klockars & S. Mastrofski, Thinking About Police. NY: McGraw-Hill.
Shapiro, B. (1993). Beyond Reasonable Doubt and Probable Cause: Historical Perspectives on the Anglo-American Law of Evidence. Sacramento: Univ.
Tetu, P. (1995). Probable Cause: Between the Police Officer and the Magistrate. Springfield: Charles Thomas.
Last updated: Aug 18, 2010
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