Chapter 1: Principles of Probable Cause and Reasonable Suspicion

Chapter structure
(1) The Required Probability

(2) Facts: The Lifeblood of Probable Cause

(3) Evaluating the Facts

(4) The “Official Channels” Rule

(5) Mistakes of Fact and Law

Related subjects covered elsewhere
Reliability of information Chapter 2 Probable Cause: Reliability of Information

Probable cause to arrest Chapter 3 Probable Cause to Arrest

Reasonable suspicion Chapter 3 Probable Cause to Arrest

Probable cause to search Chapter 4 Probable Cause to Search

Marijuana possession Chapter 22 Marijuana Searches

Definitions
Probable cause to arrest: Probable cause to arrest exists if there was a “fair probability” or “substantial chance” that the arrestee had committed the crime under investigation. See “The Required Probability” (Probable cause), below; and Chapter 3 Probable Cause to Arrest.

Probable cause to search: Probable cause to search a person, place or thing exists if there was a “fair probability” or “substantial chance” that specified evidence of a crime is now located there. See “The Required Probability” (Probable cause), below, and Chapter 4 Probable Cause to Search.

Reasonable cause: The terms “probable cause” and “reasonable cause” are synonymous.[1]

Reasonable suspicion to detain: Like probable cause to arrest and search, reasonable suspicion to detain or pat search is a judgment as to the existence and significance of incriminating evidence. The main difference is that reasonable suspicion may be based on information that is less incriminating and reliable than that which is required for probable cause.[2] Most of the principles that apply to probable cause also apply to reasonable suspicion.

The Required Probability
Probable cause: It is often assumed that probable cause requires at least a 51% chance because anything less would not be statistically “probable.” Although the Supreme Court has refused to assign a probability percentage (because it views probable cause as a non-technical standard based on common sense, not mathematical precision[3]), it has ruled that probable cause requires less than a 50% chance. Specifically, it ruled that probable cause requires neither a preponderance of the evidence (i.e. over 50%)[4] nor “any showing that such belief be correct or more likely true than false,”[5] and that it requires only a “fair probability or “substantial chance.”[6]

Reasonable suspicion: Reasonable suspicion requires only a “moderate chance,” which has been unhelpfully defined as something “considerably less” than a 50% chance.[7] A better definition is that reasonable suspicion exists if the circumstances were “consistent with” criminal activity.[8]

Facts: The Lifeblood of Probable Cause: The first thing (and sometimes the only thing) the courts look for in determining if there was probable cause is the factual basis for the officer’s belief that it exists. In fact, the Supreme Court has called this the “central teaching of this Court’s Fourth Amendment jurisprudence,” explaining that officers “must be able to point to specific and articulable facts which, taken together with rational inferences from those facts, reasonably warrant the intrusion.”[9]
Reliability of Information: Information is not factual unless there was reason to believe it was accurate. See Chapter 2 Probable Cause: Reliability of Information.

Circumstantial evidence: Probable cause may be based partly or solely on circumstantial evidence; i.e., facts from which the existence of probable cause may be inferred.[10]

Hunches and unsupported conclusions: Although hunches often play an important role in criminal investigations,[11] they are not facts and are therefore irrelevant.[12]

Information inadmissible in court
Hearsay: Hearsay may be considered,[13] but its value depends on whether there was reason to believe that it, or its source, was reliable.[14]

Privileged information: May be considered.[15]

Information obtained illegally: Will not be considered by a court in determining the existence of probable cause if it was obtained in violation of the suspect’s constitutional rights, as opposed to a violation of a state or federal statute.[16] Also see Citation Guide (Proposition 8).

Facts obtained from other officers: See “The ‘Official Channels’ Rule,” below.

Officer’s legal opinions: Although officers may make reasonable inferences, they must not provide legal opinions in their affidavits or courtroom testimony as to the significance of the facts; e.g., “These facts constitute probable cause,” or “My informant is reliable.”[17] Statements of this sort should also be avoided because they may signal a lack of training or professionalism.

Evaluating the Facts: Having ascertained the relevant facts, the courts must determine whether they add up to probable cause. Although this process is highly subjective, there are certain rules that apply, as follows:
Totality of facts: Probable cause and reasonable suspicion are based on an assessment of the overall force of the facts.[18] Thus, judges must not isolate individual facts, belittle their importance or explain them away, then conclude that probable cause did not exist because none of them were very significant.

Commonsense interpretation: The facts must be examined in light of common sense and reasonable inferences, not hypertechnical analysis.[19]

Training and experience: The courts will consider an officer’s opinion as to the meaning or significance of facts if the opinion appeared to be reasonable.[20] An officer’s opinion may have weight even if he had not qualified as an expert witness in court.[21] In listing an officer’s training and experience in an affidavit, a lengthy or detailed account is seldom necessary.[22]

Significance of multiple incriminating circumstances: The odds of having probable cause increase dramatically as the number of independent incriminating circumstances increase. To illustrate, if probable cause and reasonable suspicion could be tallied on a scorecard, and if a suspect on the street matched a general description of the perpetrator of a robbery that had just occurred nearby, we would start by giving him a PC score of two: one point because he resembled the robber and a second point because he was near the crime scene shortly after the robbery occurred. But he would also be entitled to a bonus point because the combination of these two independent circumstances is, in effect, an additional incriminating circumstance because it constitutes a “coincidence of information.”[23] In other words, when it comes to probable cause, “the whole is greater than the sum of its parts.”[24] See this endnote for examples of multiple incriminating circumstances.[25]

Possibility of an innocent explanation: It is immaterial that there might have been an innocent explanation for some or all of the circumstances upon which probable cause was based.[26]

Considering exculpatory facts: If probable cause exists, officers are not required to conduct an additional investigation to determine if there were other facts that might undermine probable cause.[27] Still, officers are “not free to disregard plainly exculpatory evidence, even if substantial inculpatory evidence (standing by itself) suggests that probable cause exists.”[28]

The “Official Channels” Rule: Probable cause may be based partly or solely on information obtained by officers via “official channels.”[29] Although officers may rely on such information, prosecutors may be required to prove that the information was accurate or reliable. See Chapter 67 Motions to Authenticate Information Source (Harvey-Madden).
What is an “official” channel? An official channel is a conduit through which information pertaining to the existence of probable cause or reasonable suspicion is routinely transmitted from one officer to another, or from a governmental agency or database to officers. Such transmissions may be formal or informal.

Formal official channels: These are well-known conduits whose primary objective is to transmit such information; NCIC, CLETS, AWS, BOLO, database communications, wanted flyers, and rollcall notifications.

Informal official channels: Information may also be transmitted on-the-fly via impromptu exchanges between officers about criminal activity, a particular crime, or a particular suspect. These communications are usually transmitted via police radios, cellphones, text messages, and face-to-face conversations.

Proof of “transmission”: The official channels rule applies only if prosecutors can prove that the information had been transmitted to, and received by, the officer who made the arrest or conducted the search.[30]

No imputed transmission: The official channels rule is sometimes referred to as the “collective knowledge” or “constructive knowledge” rule. This is misleading because it suggests that information possessed by one officer may be imputed to others without proof of transmission. This is called “post-arrest pooling” and it is not permitted.[31]

Types of transmitted information: There are two types:

Summary notifications: These are simple notifications that certain facts have been ascertained; e.g., that a warrant for the suspect’s arrest was outstanding, that the suspect was subject to parole or probation searches, that DMV records showed that a driver’s CDL was suspended.[32]

Transmission of information: These are transmissions of factual information; e.g., a physical description of the perpetrator of an armed robbery. See Chapter 2 Probable Cause: Reliability of Information (Law Enforcement Personnel).

Mistakes of Fact and Law
Mistakes of fact: If probable cause was based in whole or in part on information that was later determined to be false, the information may nevertheless be considered in determining the existence of probable cause if the officer reasonably believed it was true.[33] Examples:

Arrest of wrong person: If officers had probable cause to arrest a suspect but arrested another person by mistake, the arrest is lawful if they reasonably believed the arrestee was the suspect.[34]

Mistakes by automated license plate readers: Because automated license plate readers may misread license plate numbers, it may be unreasonable for officers to rely solely on such an alert to detain someone; e.g., officers may need to confirm that the license plate number on the stopped vehicle matched the number displayed by the reader.[35]

Mistakes of law
Reasonable mistakes: Suppression may not be appropriate if the mistake of law was reasonable.[36]

Arrest for wrong crime: See Chapter 5 Arrests (Notification Requirements, Specify crime).

No proof beyond a reasonable doubt: A search or seizure supported by probable cause is lawful, even if prosecutors refused to charge the suspect, or if a jury acquitted him.[37]

[9] QUOTES FROM: Terry v. Ohio (1968) 392 U.S. 1, 21. NOTE: Here is a good summary of the thinking process: “As information is accumulated in the process of an investigation, the police must make not a single evaluation but a series of judgments. Inevitably this is something of a balance sheet process. Some of the information, and some of the factors which they observe, will add up in support of probable cause; some, on the other hand, may undermine that support. Finally, at some point the officer must make a decision, culled from a balance of these negatives and positives, and then act on his decision.” Jackson v. US (DCC 1962) 302 F2 194, 197.

[10] USSC: New Jersey v. T.L.O. (1985) 469 US 325, 345 [“it is universally recognized that evidence, to be relevant to an inquiry, need not conclusively prove the ultimate fact in issue, but only have any tendency to make the existence of any fact that is of consequence to the determination more probable or less probable than it would be without the evidence”]. 9th CIR: US v. Diaz (9C 2007) 491 F3 1074, 1078 [“People draw reasonable conclusions all the time without direct evidence. Indeed, juries frequently convict defendants of crimes on circumstantial evidence alone.”].

[11] 9th CIR: US v. Thomas (9C 2000) 211 F3 1186, 1192 [“A hunch may provide the basis for solid police work; it may trigger an investigation that uncovers facts that establish reasonable suspicion, probable cause, or even grounds for a conviction.”].

[12] USSC: Brown v. Texas (1979) 443 US 47, 52 [the officer testified the situation “looked suspicious” but was “unable to point to any facts supporting that conclusion”]. CAL: P v. Ovieda (2019) 7 C5 1034, 1047 [“The line between a mere hunch and a reasonable suspicion based on articulable facts can be a fine one, but such a line does exist.”]; P v. Edgerrin J. (2020) 57 CA5 752, 765 [“an allegation of ‘shady’ behavior is far too vague to suggest criminal activity”]. 9th CIR: US v. Thomas (9C 2000) 211 F3 1186, 1192 [a hunch “is not a substitute for the necessary specific, articulable facts required to justify a Fourth Amendment intrusion”]. OTHER: US v. Cash (10C 2013) 733 F3 1264, 1273-74 [reasonable suspicion “must be based on something more than an inchoate and unparticularized suspicion or hunch”].

[13] USSC: Franks v. Delaware (1978) 438 US 154, 164 [“probable cause may be founded upon hearsay”]; Ker v. California (1963) 374 US 23, 36 [“That this information was hearsay does not destroy its role in establishing probable cause.”]. CAL: Mueller v. DMV (1985) 163 CA3 681, 685 [“Hearsay evidence has universally been held to establish probable cause.”]; P v. Superior Court (Bingham) (1979) 91 CA3 463, 472 [“hearsay information will support issuance of a search warrant. Indeed, the usual search warrant, based on a reliable police informer’s or citizen-informant’s information, is necessarily founded upon hearsay,” edited]; P v. Navarro (2006) 138 CA4 146, 174 [“it is inappropriate to apply the rules of evidence as a criterion to determine probable cause.”].

[14] CAL: P v. French (2011) 201 CA4 1307, 1317 [“hearsay has little value where the informant is untested and the information is uncorroborated and lacking in detail”]; P v. Superior Court (Bingham) (1979) 91 CA3 463, 473 [“whether hearsay or double hearsay information of criminal activity will support a search warrant depends not upon terminology or ritualistic formula, but upon the quality and persuasiveness of the information itself”]; P v. Love (1985) 168 CA3 104, 109-11 [“A chain is only as strong as its weakest link, so a substantial basis for crediting the hearsay statements must be provided for each level of hearsay”]. 9th CIR: US v. Angulo-Lopez (9C 1986) 791 F2 1394, 1397 [“hearsay must carry indicia of reliability”].

[15] CAL: P v. Navarro (2006) 138 CA4 146, 147 [the attorney-client privilege “is merely a rule of evidence and does not supply a constitutional right”]; P v. Morgan (1989) 207 CA3 1384, 1389 [“The rules of evidence applicable at trial do not apply in determining probable cause to arrest.”].

[16] 9th CIR: US v. Barajas-Avalos (9C 2004) 377 F3 1040, 1054 [“evidence which is obtained as a direct result of an illegal search and seizure may not be used to establish probable cause for a subsequent search”].

[17] USSC: Illinois v. Gates (1983) 462 US 213, 239 [a “wholly conclusory statement”]. 9th CIR: US v. Underwood (9C 2013) 725 F3 1076, 1092 [the affidavit “includes only two facts, foundationless expert opinion, and conclusory allegations”].

[18] USSC: District of Columbia v. Wesby (2018) __ US __ [138 S.Ct. 577, 588] [“the panel majority viewed each fact in isolation rather than as a factor in the totality of circumstances”]; Maryland v. Pringle (2003) 540 US 366, 372, fn.2 [“The court’s consideration of the money in isolation, rather than as a factor in the totality of the circumstances, is mistaken in light of our precedents.”]; US v. Sokolow (1989) 490 US 1, 9 [“Any one of these factors is not by itself proof of any illegal conduct and is quite consistent with innocent travel. But we think taken together they amount to reasonable suspicion.”]. CAL: P v. Ledesma (2003) 106 CA4 857, 863 [“The high court has repeatedly held that in determining the existence of reasonable suspicion, courts must evaluate the ‘totality of the circumstances’ on a case-by-case basis”]; P v. McFadin (1982) 127 CA3 751, 767 [“Defendant would apply the axiom that a chain is no stronger than its weakest link. Here, however, there are strands which have been spun into rope. Although each alone may have insufficient strength, and some strands may be slightly frayed, the test is whether when spun together they will serve to carry the load of upholding the action of the magistrate in issuing the warrant.”]. 9th CIR: US v. Valdes-Vega (9C 2013) 738 F3 1074, 1079 [“The nature of the totality-of-the-circumstances analysis also precludes us from holding that certain factors are presumptively given no weight without considering those factors in the full context of each particular case.”]. OTHER: US v. Edwards (5C 1978) 577 F2 883, 895 [“probable cause is the sum total of layers of information and the synthesis of what the police have heard, what they know, and what they observed as trained officers. We weigh not individual layers but the ‘laminated’ total”].

[19] USSC: Illinois v. Gates (1983) 462 US 213, 231 [“Perhaps the central teaching of our decisions bearing on the probable cause standard is that it is a practical, nontechnical conception. In dealing with probable cause, as the very name implies, we deal with probabilities. These are not technical; they are the factual and practical considerations of everyday life on which reasonable and prudent men, not legal technicians, act.”]; Massachusetts v. Upton (1984) 466 US 727, 734 [“The informant’s story and the surrounding facts possessed an internal coherence that gave weight to the whole.”]; Ryburn v. Huff (2012) 565 US 469, 476-77 [“But it is a matter of common sense that a combination of events each of which is mundane when viewed in isolation may paint an alarming picture.”]; Illinois v. Wardlow (2000) 528 US 119, 125 [“the determination of reasonable suspicion must be based on commonsense judgments and inferences about human behavior”]; Kansas v. Glover (2020) __ US __ [140 S.Ct. 1183] [“The inference that the driver of a car is its registered owner does not require any specialized training; rather, it is a reasonable inference made by ordinary people on a daily basis.”]; US v. Cortez (1981) 449 US 411, 418 [“Long before the law of probabilities was articulated as such, practical people formulated certain common sense conclusions about human behavior; jurors as factfinders are permitted to do the same—and so are law enforcement officers.”]. CAL: P v. Juarez 1973) 35 CA3 631, 636 [“Running down a street is indistinguishable from the action of a citizen engaged in a program of physical fitness. Viewed in context of immediately preceding gunshots, it is highly suspicious.”]; P v. Delgado (2022) 78 CA5 425, 429 [“The affidavit presents reasonable support for an inference police had witnessed what probably was a transfer of illegal contraband from the hangout to the SUV. This gang was in the guns-and-drugs business. The purpose of the visit probably was not social; people rarely drive in Los Angeles traffic for a social visit of three to five minutes while the driver waits in the car.”]. 9th CIR: US v. Diaz (9C 2007) 491 F3 1074, 1077 [“common sense is key”]. OTHER: US v. Pabon (2C 2017) 871 F3 164, 174 [“the officer is entitled to draw reasonable inferences on the basis of his prior experience”].

[20] USSC: Illinois v. Gates (1983) 462 US 213, 232 [“The evidence must be seen and weighed not in terms of library analysis by scholars, but as understood by those versed in the field of law enforcement.”]; US v. Arvizu (2002) 534 US 266, 273 [“This process allows officers to draw on their own experience and specialized training”]; Terry v. Ohio (1968) 392 US 1, 27 [“due weight must be given to the specific reasonable inferences which [the officer] is entitled to draw from the facts in light of his experience,” edited; US v. Cortez (1981) 449 US 411, 418 [“a trained officer draws inferences and makes deductions—inferences and deductions that might well elude an untrained person”]. CAL: P v. Ledesma (2003) 106 CA4 857, 866 [“the officer’s training and experience can be critical in translating observations into a reasonable conclusion”]; In re Frank V. (1991) 233 CA3 1232, 1240-41 [“circumstances and conduct which would not excite the suspicion of the man on the street might be highly significant to an officer who had had extensive training and experience”]; P v. Ammons (1980) 103 CA3 20, 30 [“A police officer with many years of experience acquires a certain feel for people and situations. He should not be precluded from relying on this experience where, as here, there is a wholly benevolent motive, and a rational basis for believing that circumstances tantamount to an emergency are present.”]. 9th CIR: US v. Lopez-Soto (9C 2000) 205 F3 1101, 1105 [“An officer is entitled to rely on his training and experience in drawing inferences from the facts he observes, but those inferences must also be grounded in objective facts and be capable of rational explanation.”]. BUT ALSO SEE: US v. Diaz-Juarez (9C 2002) 299 F3 1138, 1141 [an officer’s experience “may not be used to give the officers unbridled discretion in making a stop”].

[21] CAL: Wimberly v. Superior Court (1976) 16 C3 557, 565 [“It is not necessary that the officer qualify as an expert to be able to form the reasonable belief necessary to justify his actions.”]; In re Trinidad V. (1989) 212 CA3 1077, 1080 [“It was not necessary that the deputy sheriff be a qualified handwriting expert before he could describe the similarities in the writing. The issue was not whether the two writings were in fact made by the same person but only whether the deputy could reasonably suspect that they were.”].

[22] 9th CIR: US v. Garay (9C 2019) 938 F3 1108, 1113 [court rejects argument that “before the affiants’ beliefs may be taken into account, the affiants must detail the nature of their expertise”].

[23] QUOTE FROM: Illinois v. Gates (1983) 462 US 213, 222, fn.7; Ker v. California (1963) 374 US 23, 36 [“To say that this coincidence of information was sufficient to support a reasonable belief of the officers that Ker was illegally in possession of marijuana is to indulge in understatement.”]. CAL: P v. Soun (1995) 34 CA4 1499, 1523 [“The coincidence with descriptions of the assailants, and the use of a car which was, at least, ‘a very likely candidate for further investigation,’ was sufficient to justify the detention.”]; P v. Pranke (1970) 12 CA3 935, 940 [“when such remarkable coincidences coalesce, they are sufficient to warrant a prudent man in believing that the defendant has committed an offense”]. OTHER: US v. Abdus-Price (DCC 2008) 518 F3 926, 930 [a “confluence” of factors]; US v. Carney (6C 2012) 675 F3 1007 [“interweaving connections”].

[24] QUOTE FROM: District of Columbia v. Wesby (2018) __ US __ [138 S.Ct. 577, 588].

[25] EXAMPLES: The following combinations of facts have been held sufficient to provide probable cause or reasonable suspicion:

• The number of suspects in the vehicle corresponded with the number of people who had just committed the crime. P v. Soun (1995) 34 CA4 1499, 1523 [“The coincidence with descriptions of the assailants, and the use of a car which was, at least, ‘a very likely candidate for further investigation,’ was sufficient to justify the detention.”].

• “The male was wearing a white shirt and the female was wearing a green dress.” P v. Little (2012) 206 CA4 1364, 1370.

• Suspect’s physical description plus he did something that tended to demonstrate consciousness of guilt, such as lying to officers, making a furtive gesture, reacting unusually to the officer’s presence, or attempting to elude officers. See P v. Fields (1984) 159 CA3 555, 564.

• Suspect’s physical description plus he was found in possession of the fruits or instrumentalities of the crime. P v. Hagen (1970) 6 CA3 35, 43.

• Robber and the suspect were (1) light-skinned black males, (2) approximately 40 years old, (3) over six feet tall, (4) wearing a white straw hat, (5) wearing dark pants, and (5) wearing light shirt. P v. Adams (1985) 175 CA3 855, 859, 861.

• “The description of the assailant was more than a general description; it provided several unique distinguishing features—sex, height, race, age, and attire.” P v. Fields (1984) 159 CA3 555, 564.

• Suspect’s physical description plus being in a car similar in appearance to the car used by the perpetrator. P v. Hill (2001) 89 CA4 48, 55.

• “The descriptions significantly matched as to age, height, weight, sex, race, and the bag being carried.” In re Brian A. (1985) 173 CA3 1168, 1174 [“Where there were two perpetrators and an officer stops two suspects who match the descriptions he has been given, there is much greater basis to find sufficient probable cause for arrest. The probability of there being other groups of persons with the same combination of physical characteristics, clothing, and trappings is very slight.”].

• The officer “had received a reliable, though generic, description of the number of suspects and their race, gender, clothing, and approximate location, as well as information about the direction in which they were heading. Taken in the ensemble, these facts were sufficient to give rise to a reasonable suspicion that the appellant and his companion were the robbers.” US v. Arthur (1C 2014) 764 F3 92, 97-98. Edited.

• Suspect’s physical description plus the suspect was in the company of a person who was positively identified as one of two men who had just committed a crime. P v. Bowen (1987) 195 CA3 269, 274.

• Suspect’s physical description plus he was detained shortly after the crime occurred at the location where the perpetrator was last seen or on a logical escape route. P v. Atmore (1970) 13 CA3 244, 246 [“[The officer] was informed of the approximate age of the suspect and of the fact that he was supposed to be wearing a dark jacket. More important, perhaps, the murder mentioned in the broadcast had evidently just been committed and defendant was walking away from the scene of its commission.”].

• In the defendant’s stopped car, an officer saw a “bladder device” commonly used to cheat on a urine drug test, plus the officer was aware that the suspect was en route to take a probation drug test. US v. Cash (10C 2013) 733 F3 1264, 1275.

• Others: In re Carlos M. (1990) 220 CA3 372, 382 [“where, as here, a crime is known to have involved multiple suspects, some of whom are specifically described and others whose descriptions are generalized, a defendant’s proximity to a specifically described suspect, shortly after and near the site of the crime, provides reasonable grounds to detain for investigation a defendant who otherwise fits certain general descriptions”]; US v. Abdus-Price (DCC 2008) 518 F3 926, 930-31 [suspect and perpetrator were in vehicles of the same make and model, and both with tinted windows and a dark-colored top with light-colored side]; P v. Anthony (1970) 7 CA3 751, 763 [suspect’s physical description plus clothing similar to that of the perpetrator]; Chambers v. Maroney (1970) 399 US 42, 46-47; P v. Joines (1970) 11 CA3 259, 263 [“The fact that there were two persons fitting descriptions given for the two suspects narrowed the chance of coincidence.”]; Colorado v. Bannister (1980) 449 US 1, 4 [number of suspects and their general description plus lug nuts in plain view in car provided probable cause to arrest for theft of lug nuts that had just occurred]; P v. Britton (2001) 91 CA4 1112, 1118-19 [“This evasive conduct by two people instead of just one person, we believe, bolsters the reasonableness of the suspicion”].

[26] USSC: District of Columbia v. Wesby (2018) __ US __ [138 S.Ct. 577, 588] [“the panel mistakenly believed that it could dismiss outright any circumstances that were susceptible of innocent explanation” but probable cause does not require officers to rule out a suspect’s innocent explanation for suspicious facts,” edited]; Kansas v. Glover (2020) __ US __ [140 S.Ct. 1183] [although it is possible that the driver of a car was not the registered owner, the conclusion is nevertheless reasonable, absent reason to believe otherwise]; US v. Arvizu (2002) 534 US 266, 277 [“A determination that reasonable suspicion exists need not rule out the possibility of innocent conduct.”]; Illinois v. Wardlow (2000) 528 US 119, 126 [the Constitution “accepts the risk that officers may stop innocent people.”]; New Jersey v. T.L.O. (1985) 469 US 325, 346 [“it is irrelevant that other [innocent] hypotheses were also consistent”]. CAL: P v. Brown (2015) 61 C4 968, 985 [the possibility of an innocent explanation “does not deprive the officer of the capacity to entertain a reasonable suspicion of criminal conduct”]; P v. Glaser (1995) 11 C4 354, 373 [“What is required is not the absence of innocent explanation, but the existence of “specific and articulable facts which, taken together with rational inferences from those facts, reasonably warrant that intrusion.”]; P v. Ledesma (2003) 106 CA4 857, 863 [“[The Supreme Court] has been sharply critical of lower court decisions precluding police reliance on facts consistent with an innocent as well as a guilty explanation.”]. 9th CIR: Garcia v. County of Merced (9C 2011) 639 F3 1206, 1209 [the information “does not have to be conclusive of guilt, and it does not have to exclude the possibility of innocence”. OTHER: US v. Clark (11C 2022) 32 F4 1080, 1088 [“the question is not whether there is an innocent explanation for Clark’s behavior, but rather whether there was probable cause”]; US v. Patterson (2C 2022) 25 F4 123, 140 [“Reasonable suspicion does not require officers to disprove every innocent possibility before investigating suspicious circumstances”]; US v. White (6C 2021) 990 F3 488, 492 [“Probable cause does not demand resolving each jot and tittle of metaphysical doubt”]; US v. Reyes (5C 2020) 963 F3 482, 489 [“Although Reyes may have an innocent explanation for each of her actions, they together gave [the officer] much more than a mere ‘hunch’ of illegal activity,” edited.]; US v. Blakeney (4C 2020) 949 F3 851, 859 [immaterial that affidavit failed to “rule out” other explanations for a fatal accident].

[27] USSC: Baker v. McCollan (1979) 443 US 137, 145-46 [“we do not think a sheriff executing an arrest warrant is required by the Constitution to investigate independently every claim of innocence”]. CAL: Hamilton v. City of San Diego (1990) 217 CA3 838, 845 [“where probable cause to arrest has been established, we are not aware of any authority which suggests police officers must conduct some additional investigation before incarcerating a suspect”]. OTHER: US v. Pabon (2C 2017) 871 F3 164, 176 [“Given the fluidity purposely built into the probable cause standard, requiring officers continually to make moment-to-moment assessments of probable cause could misallocate limited police resources and even undermine the framework established in Gerstein and McLaughlin, which provides for a prompt determination by a magistrate whether probable cause exists as a prerequisite to extended restraint of liberty following arrest.”]; Gilmore v. City of Minneapolis (8C 2016) 837 F3 827, 833 [“an officer need not conduct a ‘mini-trial’ before effectuating an arrest although he cannot avoid minimal further investigation if it would have exonerated the suspect”]; Ricciuti v. NYC Transit Authority (2C 1997) 124 F3 123, 128 [“Once a police officer has a reasonable basis for believing there is probable cause, he is not required to explore and eliminate every theoretically plausible claim of innocence before making an arrest.”]; Gardenhire v. Schubert (6C 2000) 205 F3 303, 318 [“this court is not adding a duty to investigate as a factor for the establishment of probable cause”]; US v. Daigle (8C 2020) 947 F3 1076, 1081 [“the affidavit is judged on the adequacy of what it does contain, not on what it lacks”].

[28] QUOTE FROM: Goodwin v. Conway (3C 2016) 836 F3 321, 328. OTHER: US v. Pabon (2C 2017) 871 F3 164, 175 [officers may not “disregard facts tending to dissipate probable cause when confronted with such facts before an arrest is made”].

[29] USSC: US v. Hensley (1985) 469 US 221, 231 [“effective law enforcement cannot be conducted unless police officers can act on directions and information transmitted by one officer to another and that officers, who must often act swiftly, cannot be expected to cross-examine their fellow officers about the foundation for the transmitted information”]; CAL: P v. Soun (1995) 34 CA4 1499, 1521, 1523-24 [“a police officer who receives a request or direction, through police channels, to detain named or described individuals may make a constitutionally valid detention, even without personal knowledge of facts sufficient to justify the detention, so long as the facts known to the police officer or agency that originated the request would be sufficient”]. 9th CIR: Case v. Kitsap County Sheriff (9C 2001) 249 F3 921 [“an NCIC hit, although not definitive in terms of conviction, has been routinely accepted in establishing probable cause for a valid arrest”]; US v. Jensen (9C 2005) 425 F3 698, 704 [“The accepted practice of modern law enforcement is that an officer often makes arrests at the direction of another law enforcement officer even though the arresting officer himself lacks actual, personal knowledge of the facts supporting probable cause.”]. OTHER: US v. Baker (6C 2020) 976 F3 636, 643 [“But if probable cause existed for the warrant, an officer may arrest the suspect without personally learning the facts establishing probable cause. This ‘common sense’ conclusion minimizes the volume of information concerning suspects that must be transmitted to other jurisdictions and enables police in one jurisdiction to act promptly in reliance on information from another jurisdiction.”]; US v. Latorre (10C 2018) 893 F3 744, 755 [officers “should be able to reasonably rely on the information provided by other officers without having to cross-examine them about the foundation of the transmitted information”]; US v. Valez (2C 1986) 796 F2 24, 28 [“The rule exists because, in light of the complexity of modern police work, the arresting officer cannot always be aware of every aspect of an investigation; sometimes the authority to arrest a suspect is based on facts known only to his superior or associates”]; US v. Babilonia (2C 2017) 854 F3 163, 178 [“under the collective knowledge doctrine, even if the law enforcement officer actually conducting the search lacks the relevant facts to support probable cause, the search may nonetheless be permissible if the officer acted on the assessment or instructions of other officers who did have such facts”]; US v. Lyons (6C 2012) 687 F3 754, 769 [“Responding officers are entitled to presume the accuracy of the information furnished to them by other law enforcement personnel.”].

[30] CAL: P v. Rice (1967) 253 CA2 789, 792 [“The People must prove not only that the collective knowledge of the investigating authorities justified the arrest, but that such knowledge was funneled to the arresting officer by imparting it to him or, more simply, by the giving of an order or request to make the arrest by someone who, in turn, was possessed of such collective knowledge.”].

[31] CAL: P v. Coleman (1968) 258 CA2 560, 563, fn.2 [“The police cannot pool their information after an arrest made on insufficient cause.”]; P v. Adams (1985) 175 CA3 855, 862 [“warrantless arrest or search cannot be justified by facts of which the officer was wholly unaware at the time”]; P v. Superior Court (Haflich) (1986) 180 CA3 759. 766 [“The issue of probable cause depends on the facts known to the officer prior to the search.”]. 9th CIR: John v. City of El Monte (9C 2008) 515 F3 936, 940 [“The determination whether there was probable cause is based upon the information the officer had at the time of making the arrest.”]. OTHER: US v. Massenburg (4C 2011) 654 F3 480, 493 [if post-detention pooling was permitted “it would be irrelevant that no officer had sufficient information to justify a search or seizure”]; US v. Latorre (10C 2018) 893 F3 744, 754 [this was not a case of after-the-fact pooling of information”]. NOTE: There is language in some cases (below), even from the Supreme Court, that might be interpreted to mean that the collective knowledge rule applies even if the officer with the incriminating information had neither communicated that information to the officer who acted upon it, nor requested that the officer act upon it. Such an interpretation is undoubtedly wrong as it would permit post-arrest pooling. See Illinois v. Andreas (1983) 463 US 765, 771, fn.5 [“where law enforcement authorities are cooperating in an investigation, as here, the knowledge of one is presumed shared by all”]; US v. Hoyos (9C 1989) 892 F2 1387, 1392 [“Probable cause may be based on the collective knowledge of all of the officers involved in the investigation”]. COMPARE: US v. Shareef (10C 1996) 100 F3 1491, 1503 [“the information had not been shared”]; Dyke v. Taylor Implement Mfg. Co. (1968) 391 US 216, 222 [officer “had not been told that Harris and Ellis had identified the car from which shots were fired as a 1960 or 1961 Dodge.”].

[32] CAL: P v. Ramirez (1997) 59 CA4 1548 [“officers and investigators need not inform the final arresting officer of the precise nature of the probable cause they possess”]; P v. Soun (1995) 34 CA4 1499, 1523-24 [“a police officer who receives a request or direction, through police channels, to detain named or described individuals may make a constitutionally valid detention, even without personal knowledge of facts sufficient to justify the detention, so long as the facts known to the police officer or agency that originated the request would be sufficient”]; P v. Lara (1967) 67 C2 365, 374 [officer was “entitled to make an arrest” based on a request by another agency]. 9th CIR: US v. Ramirez (9C 2007) 473 F3 1026, 1037 [“Where one officer knows facts constituting reasonable suspicion or probable cause and he communicates an appropriate order or request, another officer may conduct a warrantless stop, search, or arrest without violating the Fourth Amendment,” edited.]. OTHER: US v. Nafzger (7C 1992) 974 F2 906, 913 [“If the officer issuing the flyer or bulletin concludes that the facts he is aware of authorize a stop or arrest and relays that conclusion to another officer, that officer may rely on the conclusion, regardless of whether he knows the supporting facts.”].

[33] USSC: Illinois v. Rodriguez (1990) 497 US 177, 185 [“what is generally demanded of the many factual determinations that must regularly be made by agents of the government … is not that they always be correct, but that they always re reasonable”]. 9th CIR: US v. Mariscal (9C 2002) 285 F3 1127, 1131 [“a mere mistake of fact will not render a stop illegal, if the objective facts known to the officer gave rise to a reasonable suspicion that criminal activity was afoot”].

[34] OTHER: US v. Patrick (8C 2015) 776 F3 951, 955 [officers “reasonably” but mistakenly “believed the man driving the gold-brown Buick” was a fugitive]; Catlin v. City of Wheaton (7C 2009) 574 F3 361, 366 [officers “are required to show only the reasonableness of their belief that the person they arrested was the person they were seeking”].

[35] 9th CIR: Green v. City of San Francisco (9C 2014) 751 F3 1039, 1045.

[36] USSC: Heine v. North Carolina (2014) 574 US 54, 66 [“The Fourth Amendment tolerates only reasonable mistakes, and those mistakes—whether of fact or of law—must be objectively reasonable.”]. CAL: P v. Campuzano (2015) 237 CA4 Supp.1 14, 21 [“There was no prior guidance for the officers in interpreting the ordinance.”]. OTHER: US v. Monell (1C 2015) 801 F3 34, 42 [“And the exclusionary rule does not exist to punish such negligent, harmless mistakes by law enforcement.”]. NOTE: Heien apparently abrogates, or at least calls into question, the rulings in the cases that did not consider the reasonableness of the officer’s mistakes; e.g., P v. Teresinski (1982) 30 C3 822, 831; P v. Reyes (2011) 196 CA4 856, 863.

[37] CAL: P v. Case (1980) 105 CA3 826, 831 [“the law of arrest envisions that persons will be arrested who are not ultimately prosecuted or convicted”]; P v. Burgess (1959) 170 CA2 36, 41 [“an acquittal, or conviction of appellant has no bearing on the legality of the arrest”]. OTHER: Powe v. City of Chicago (7C 1981) 664 F2 639, 647 [the existence of probable cause “is of course sufficient reason to make an arrest, even if the arrestee should later be found innocent”].