Chapter 1: Principles of Probable Cause and Reasonable Suspicion 

[1] USSC:
Heien v. North Carolina (2014) 574 US 54

[2] USSC:
Arizona v. Johnson (2009) 555 US 323, 330 [a reasonable
suspicion of criminal activity is one that is "reasonably
grounded, but short of probable cause"]. ALSO SEE:
P v. Ledesma (2003) 106 CA4 857, 863 ["reasonable suspicion
is an abstract concept, not a 'finely tuned standard' and
deliberately avoided encumbering its determination with a neat set
of legal rules"].

[3] USSC: Maryland v.
Pringle (2003) 540 US 366, 371 ["The probable cause
standard is incapable of precise definition or quantification into
percentages because it deals with probabilities and depends on the
totality of circumstances."]; US v.
Sokolow (1989) 490 US 1, 7 [reasonable suspicion "is not
readily, or even usefully, reduced to a neat set of legal rules"].
OTHER: US v. Baker (6C 2020) 976 F3 636, 645 [the
Supreme Court "has refused to offer clear rules separating the
hazy border between suspicion and probable cause"]; US
v. Melvin (1C 1979) 596 F2 492, 495
["appellant reads the phrase 'probable cause' with emphasis on the
word 'probable,' and would define it mathematically to mean 'more
likely than not' or 'by a preponderance of the evidence.' This
reading is incorrect."].

[4] CAL: P v. Westerfield (2019)
6 C5 632, 659] [probable cause "is less than a preponderance of
the evidence or even a prima facie case"]; P v.
Carrington (2009) 47 C4 145, 163 ["The showing required in
order to establish probable cause is less than a preponderance of
the evidence or even a prima facie case."]. OTHER:
US v. Garcia (5C 1999) 179 F3 265, 269 ["more than bare
suspicion, but need not reach the fifty percent mark"]; US
v. Ortiz (4C 2012) 669 F3 439, 446 [probable cause
"is less demanding than a standard requiring preponderance of the
evidence"]. ALSO SEE: Herring v.
US (2009) 555 US 135, 139 ["The very phrase 'probable
cause' confirms that the Fourth Amendment does not demand all
possible precision."]; Valdez v.
McPheters (10C 1999) 172 F3 1220, 1227, fn.5 ["probable
cause itself is a relatively low threshold of proof"]; US
v. $42,500 (9C 2002) 283 F3 977, 980 ["probable
cause is not an exacting standard"].

[5] QUOTE FROM: Texas v.
Brown (1983) 460 US 730, 742.

[6] QUOTES FROM:
Safford Unified School District v. Redding (2009) 557 US
364, 371. USSC: Illinois v. Gates (1983) 462 US 213,
243, fn.13. CAL: Bailey v.
Superior Court (1992) 11 CA4 1107, 1111 ["Probable cause to
issue an arrest or search warrant [exists if] there is a fair
probability that a person has committed a crime, or a place
contains contraband or evidence of a crime."]; P v.
Rosales (1987) 192 CA3 759, 767-68 [the "fair probability"
standard applies to both probable cause to search and probable
cause to arrest]. 9th CIR: Garcia v.
County of Merced (9C 2011) 639 F3 1206, 1209 ["All that is
required is a 'fair probability'"]. OTHER:
US v. Centeno-Gonzalez (1C 2021) 989 F3 36, 45 [probable
cause "does not require law enforcement officers to have an
ironclad case on the proverbial silver platter"];
US v. Howard (7C 2018) 883 F3 703, 707 ["Probable cause
does not require an actual showing of criminal activity, or even
that the existence of criminal activity is more likely true than
not; instead, probable cause merely requires that a probability or
substantial chance of criminal activity exists."]. NOTE:
"Honest and strong suspicion": In the past, the courts
would say that probable cause to arrest requires an "honest and
strong suspicion" that the suspect had committed a crime. This
definition is seldom used. See Peng v. Hu (9C
2003) 335 F3 970, 976 [the "honest and strong suspicion" test and
the "fair probability" test are "very similar"].

[7] USSC: Kansas v. Glover (2020)
__ US __ [140 S.Ct. 1183] [reasonable suspicion "falls
considerably short of 51% accuracy for, as we have explained, 'to
be reasonable is not to be perfect'"];
Safford Unified School District v. Redding (2009) 557 US
364, 371 ("moderate chance"); Illinois v. Wardlow (2000)
528 US 119, 123 ["'reasonable suspicion' is a less demanding
standard than probable cause and requires a showing considerably
less than preponderance of the evidence"];
US v. Arvizu (2002) 534 US 266, 274 [reasonable suspicion
"falls considerably short of satisfying a preponderance of the
evidence standard"]; Alabama v. White (1990) 496 US 325,
330 ["Reasonable suspicion is a less demanding standard than
probable cause not only in the sense that reasonable suspicion can
be established with information that is different in quantity or
content than that required to establish probable cause, but also
in the sense that reasonable suspicion can arise from information
that is less reliable than that required to show probable
cause."]. OTHER: US v. Jeter (6C 2013) 721 F3 746,
751 ["Reasonable suspicion exists where the officer can articulate
specific, particularized facts that amount to more than a 'hunch'
that criminal activity may be afoot."]; US v. Santillan (2C
2018) 902 F3 49, 56 ["The reasonable suspicion standard is not
high and is less demanding than probable cause, requiring only
facts sufficient to give rise to a reasonable suspicion that
criminal activity may be afoot."]; US v. Latorre (10C 2018)
893 F3 744, 751 ["reasonable suspicion may exist even if it is
more likely than not that the individual is not involved in any
illegality. This is because reasonable suspicion requires
considerably less than proof of wrongdoing by a preponderance of
the evidence"]. NOTE: Officers may detain two or more
people for a crime committed by only one person if reasonable
suspicion exists for each. P v. Rodriguez (1987) 196 CA3
1041, 1048. NOTE: Reasonable suspicion is also known as
"reasonable cause," "particularized suspicion," "articulable and
individualized suspicion," and "founded suspicion." See
In re Randy G. (2001) 26 C4 556, 567.

[8] QUOTE FROM: P v.
Souza (1994) 9 C4 224, 233 ["when circumstances are
consistent with criminal activity, they permit—even demand—an
investigation"]. CAL: Kodani v.
Snyder (1999) 75 CA4 471,476-77.

[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"].