FOR PUBLICATION
 UNITED STATES COURT OF APPEALS
      FOR THE NINTH CIRCUIT

UNITED STATES OF AMERICA,                  No. 06-30368
                Plaintiff-Appellee,
               v.                            D.C. No.
                                          CR-05-00074-BLW
JUSTIN WELLS GRIGG,
                                              OPINION
             Defendant-Appellant.
                                      
       Appeal from the United States District Court
                 for the District of Idaho
        B. Lynn Winmill, District Judge, Presiding

                  Argued and Submitted
             March 6, 2007—Portland, Oregon

                   Filed August 22, 2007

      Before: Ronald M. Gould, Richard A. Paez, and
          Johnnie B. Rawlinson, Circuit Judges.

                 Opinion by Judge Gould




                           10245
10248               UNITED STATES v. GRIGG


                         COUNSEL

Thomas Monaghan, Federal Defenders of Eastern Washing-
ton and Idaho, Boise, Idaho, for defendant-appellant Justin
Wells Grigg.

Aaron N. Lucoff, Assistant United States Attorney, Boise,
Idaho, for plaintiff-appellee the United States.


                         OPINION

GOULD, Circuit Judge:

   Appellant-Defendant Justin Wells Grigg appeals the district
court’s denial of his motion to suppress an unregistered auto-
matic firearm that police officers discovered while conducting
an investigative stop of Grigg pursuant to a citizen’s com-
plaint that Grigg had been playing his car stereo at an exces-
sive volume earlier in the day. We have jurisdiction under 28
U.S.C. § 1291. We reverse the district court’s denial of the
motion to suppress the firearm and post-arrest statements and
remand for further proceedings.

                               I

  On April 12, 2005, a grand jury returned a one-count
indictment in the United States District Court for the District
                    UNITED STATES v. GRIGG               10249
of Idaho, charging Grigg with possession of an unregistered
firearm, an SKS automatic rifle (machine gun), in violation of
26 U.S.C. § 5861(d). Police officers in Nampa, Idaho had dis-
covered the weapon during an investigatory stop that occurred
because they suspected Grigg of playing his car stereo at an
excessive volume earlier in the day in violation of a local
noise ordinance.

   On August 15, 2005, Grigg filed a motion to suppress the
firearm and statements that he made after the stop. Grigg
claimed that the Nampa police violated his Fourth Amend-
ment rights by conducting a search of his vehicle solely on the
basis of suspicion that he had committed a misdemeanor by
playing his car stereo at excessive volume earlier in the day.
On September 19 and 20, 2005, the district court held a hear-
ing on Grigg’s motion to suppress. The following facts were
established:

   On September 21, 2004, a Nampa resident, Jeffrey Harmel,
called the police to report that a car had driven by his house
at 710 Dufur Street with its car stereo playing very loudly.
Officers Oren McGuire and Mike Roeder of the Nampa
Police Department responded independently. Upon Officer
McGuire’s arrival, Harmel said that “kids” in the neighbor-
hood had been harassing him with loud music for “years,” and
that he had “caught” the car in question — a Mercury Cougar,
the driver of which was Grigg — “booming” music several
times in the preceding days, and that on one occasion he had
called the police to file a complaint. Although Harmel testi-
fied that he did not know whether the police responded to the
previous complaint, according to Officer McGuire’s testi-
mony, the police had given Grigg a prior verbal warning.

   While filling out a formal citizen complaint, Harmel
pointed down the street to where the offending car was parked
in front of a house at 1800 East Dewey Street. During this
conversation, about one minute after Officer McGuire’s
arrival, Grigg got in the Cougar and drove back toward Har-
10250                   UNITED STATES v. GRIGG
mel and Officer McGuire. As Grigg passed, no music could
be heard and he was driving lawfully, but Harmel identified
Grigg as the subject of his complaint. At that point, although
Officer McGuire had not ascertained Grigg’s identity or
investigated possible prior complaints, McGuire told Officer
Roeder, who had arrived, to stop the car to inquire about
excessive noise, determine the driver’s identity, and serve the
driver with a citation and summons. Officer McGuire then
completed the complaint form, which Harmel signed, leaving
blank the unknown personal information about the subject of
the complaint.

   On Officer McGuire’s instruction, Officer Roeder spotted
the Cougar and trailed Grigg. Roeder activated his overhead
lights, and Grigg delayed a few seconds before pulling into a
driveway. After the stop, Grigg started to get out of his car,
but Officer Roeder ordered him back inside. As Officer
Roeder approached, Grigg volunteered that he had a “hunting
rifle” inside the car that he was taking to get “fixed.” Officer
Roeder then observed the SKS rifle on the passenger seat
along with ammunition and .380 caliber handgun shells.
Roeder then initiated a pat down search and arrested Grigg
after finding concealed brass knuckles.1

   At the suppression hearing, Officer McGuire testified that
he did not intend to arrest Grigg for the suspected misdemea-
nor noise violation because under Idaho law he could not
arrest a suspect for a misdemeanor not committed in his pres-
ence.2 Officer McGuire testified that he did not inquire with
  1
     On a motion in limine, the district court later excluded the .380 caliber
shells. Although it did not on that motion exclude the brass knuckles, the
record contains no indication that the government ever moved to admit
them.
   2
     See Idaho Code Ann. § 19-603 (2007) (“When peace officer may
arrest”) (“A peace officer may make an arrest in obedience to a warrant
delivered to him, or may, without a warrant, arrest a person: [1] For a pub-
lic offense committed or attempted in his presence; [2] When a person
arrested has committed a felony, although not in his presence; [3] When
a felony has in fact been committed and he has reasonable cause for
believing the person arrested to have committed it . . . .”).
                    UNITED STATES v. GRIGG                 10251
dispatch to check whether in making the prior complaint Har-
mel had given the license number of the Cougar. Officer
McGuire testified further that under Nampa Police Depart-
ment protocol, a record would exist of Harmel’s previous
complaint, including any prior contact with Grigg and any
verbal warning he received. Officer McGuire testified that
any specific information included in the log, such as a sub-
ject’s name and address, would have been provided by the
previous complainant. Officer McGuire also testified that it
would have been time-consuming to attempt to bring up the
log on his patrol car computer, and that he did not want to
“bother” dispatch with a noise complaint, which “is not that
big of a deal.” Officer McGuire further testified that he
decided to stop the Cougar because all the parties involved
were present. Addressing whether there was an alternate
method of identifying the driver, Officer McGuire stated that
a call to the dispatch was unreliable because the name of the
driver could have been provided only by Harmel, who did not
know Grigg’s name. Officer McGuire conceded, however,
that absent the ability to stop the Cougar directly, a preferred
method would have been to return to the address where the
Cougar was parked at 1800 East Dewey Street and ask about
the driver’s identity.

   The district court determined that (1) the investigating offi-
cers did not know the identity or residence of the driver of the
Cougar, (2) the driver was in the process of driving away
before the stop, and (3) the officers sought to stop the driver
to gain more information about Harmel’s noise complaint and
identify the driver. The district court rejected the govern-
ment’s proffered alternate theories for the stop: 1) it was not
to undertake a citizen’s arrest because Harmel had not
expressed a desire that the driver be arrested; 2) it was not an
attempt to serve Harmel’s complaint and a summons on Grigg
because Officer McGuire was still in the process of complet-
ing the complaint when the Cougar drove past; 3) and the
government did not meet its evidentiary burden that Grigg
played loud music in the presence of Officer Roeder, which
10252                   UNITED STATES v. GRIGG
would have provided probable cause to stop Grigg for a pres-
ent noise violation. The district court concluded from these
findings that Officers McGuire and Roeder conducted an
investigative stop under Terry v. Ohio, 

(1968),
based on a citizen complaint to gather information on the
alleged completed noise violation.

   Because the criminal conduct that the officers were investi-
gating had already occurred, the district court held that United
States v. Hensley, 

(1985), applied even though
that case concerned an investigatory stop based on reasonable
suspicion that the defendant had previously committed a fel-
ony (armed robbery). See 

229. In conducting the
balancing test set forth in Hensley between the law enforce-
ment interest in crime prevention and an individual’s interest
in personal security from governmental intrusion, see 

the district court found important that the officers did not
know the identity of Grigg and had no certain way of locating
him when faced with the likelihood that the driver of the Cou-
gar had committed an excessive noise violation and was leav-
ing the area. The district court rejected Grigg’s arguments that
the police had other less intrusive means of identifying him —
such as requesting specific information from the police logs
on Harmel’s previous complaint or checking the residence
where Grigg had parked his car — due to the unreliability of
these sources of information. Although commenting that it
was “a very, very close call,” the district court held in favor
of the government that the stop was a reasonable method of
resolving the noise complaint.

   After the district court denied Grigg’s motion to suppress,
the case proceeded to trial, and on November 18, 2005, a jury
found Grigg guilty of violating 26 U.S.C. § 5861(d) for know-
ingly possessing the unregistered SKS automatic rifle. Grigg
timely appealed.3
  3
    In this appeal, Grigg challenges the district court’s denial of his motion
to suppress the firearm and other evidence, and also contends that the trial
verdict cannot stand because of prosecutorial misconduct.
                    UNITED STATES v. GRIGG               10253
                              II

   The reasonableness of an investigatory stop is reviewed de
novo. See United States v. $109,179 in U.S. Currency, 

, 1083-84 (9th Cir. 2000). Such a stop must be
based on reasonable suspicion under the totality of the cir-
cumstances. United States v. Fernandez-Castillo, 

, 1117 (9th Cir. 2003). Any underlying factual findings
are reviewed for clear error. United States v. Colin, 

, 442 (9th Cir. 2002).

                              III

   Most of the constitutional principles at play in this appeal
are well established. The Fourth Amendment protects the
“right of the people to be secure in their persons, houses,
papers, and effects against unreasonable searches and sei-
zures.” U.S. Const. Amend. IV. Under Terry and its progeny,
police may, consistent with the Fourth Amendment, stop per-
sons in the absence of probable cause under limited circum-
stances. See Dunaway v. New York, 

, 207-11
(1979). In particular, law enforcement officers may briefly
stop a moving automobile to investigate a reasonable suspi-
cion that its occupants are involved in criminal activity. See
United States v. Brignoni-Ponce, 

, 881 (1975);
United States v. Hartz, 

, 1017 (9th Cir. 2006);
United States v. Sigmond-Ballesteros, 

, 1121-
22 (9th Cir. 2002). However, the governmental interest in
investigating possible criminal conduct based on an officer’s
reasonable suspicion may be outweighed by the Fourth
Amendment interest of the driver in remaining secure from
the intrusion. See Delaware v. Prouse, 

, 654-55
(1979).

   [1] An investigatory stop can be undertaken to prevent
ongoing or imminent crime, i.e., when a police officer “ob-
serves unusual conduct which leads him reasonably to con-
clude in light of his experience that criminal activity may be
10254                   UNITED STATES v. GRIGG
afoot.” 

; see also United States v. Arvizu,

, 273 (2002). Further, in Hensley, the United
States Supreme Court held that “if police have a reasonable
suspicion, grounded in specific and articulable facts, that a
person they encounter was involved in or is wanted in connec-
tion with a completed felony, then a Terry stop may be made
to investigate that 

(emphasis
added). The Hensley court explicitly confined its analysis to
the felony context, leaving open the question whether the rule
could be extended to “all past crimes, however serious,” i.e.,
misdemeanors. 

Supreme Court’s Hensley deci-
sion did not answer the issue tendered by this appeal. Grigg’s
challenge to the district court’s extension of Hensley raises an
issue of first impression for us.4

                                    A

   In Hensley, the investigative stop arose after two armed
men robbed a tavern in the Cincinnati suburb of St. Bernard,
Ohio, and the police department there learned that Hensley
was the getaway 

. The St. Bernard
police department issued a “wanted flyer” that described
Hensley and the date and location of the alleged robbery, with
a request that other police departments in the Cincinnati met-
ropolitan area pick up and hold Hensley in the event that he
were located. 

warned that Hensley should be
considered armed and dangerous. 

after the
robbery, police officers in Covington, Kentucky, who were
familiar with Hensley, noticed him in the driver’s seat of a
Cadillac and notified dispatch. 

Another pair of
Covington officers heard the call, radioed that they had seen
the wanted flyer about Hensley, and one of the officers drove
  4
    Of our sister circuits, only the Sixth Circuit has addressed this issue,
stating that the Hensley rule did not apply to past completed misdemea-
nors. See Gaddis v. Redford Twp., 

, 771 n.6 (6th Cir. 2004)
(“Police may . . . make a stop when they have reasonable suspicion of a
completed felony, though not of a mere completed misdemeanor.”).
                    UNITED STATES v. GRIGG               10255
to an apartment where Hensley was known to stay. 

When the Cadillac was again spotted, one of the Covington
officers pulled over Hensley and, during the stop, discovered
a weapon. 

arrested for being a convicted
felon in possession of a firearm. 

   Upholding the district court’s denial of Hensley’s motion to
suppress the firearm, the Supreme Court employed a balanc-
ing test to weigh “the nature and quality of the intrusion on
personal security against the importance of the governmental
interests alleged to justify the intrusion.” 

228.
Acknowledging the differences between investigating past
criminal conduct and detecting ongoing or imminent crime,
the Supreme Court recognized that the exigencies involved in
crime prevention are attenuated in the context of completed
past crimes:

    A stop to investigate an already completed crime
    does not necessarily promote the interest of crime
    prevention as directly as a stop to investigate sus-
    pected ongoing criminal activity. Similarly, the exi-
    gent circumstances which require a police officer to
    step in before a crime is committed or completed are
    not necessarily as pressing long afterwards. Public
    safety may be less threatened by a suspect in a past
    crime who now appears to be going about his lawful
    business than it is by a suspect who is currently in
    the process of violating the law. Finally, officers
    making a stop to investigate past crimes may have a
    wider range of opportunity to choose the time and
    circumstances of the stop.

However, the Supreme Court stressed that the
law enforcement interest in solving crime might, in some situ-
ations, permit an investigatory stop for a past crime:

    Despite these differences, where police have been
    unable to locate a person suspected of involvement
10256               UNITED STATES v. GRIGG
    in a past crime, the ability to briefly stop that person,
    ask questions, or check identification in the absence
    of probable cause promotes the strong government
    interest in solving crimes and bringing offenders to
    justice. Restraining police action until after probable
    cause is obtained would not only hinder the investi-
    gation, but might also enable the suspect to flee in
    the interim and to remain at large. Particularly in the
    context of felonies or crimes involving a threat to
    public safety, it is in the public interest that the crime
    be solved and the suspect detained as promptly as
    possible.

   Grigg argues that Hensley is distinguishable on its facts
because that case concerned a completed felony, an armed
robbery, that presented a significant public safety risk,
whereas Grigg’s suspected misdemeanor noise violation is a
minor nuisance. In urging us to consider the nature of Grigg’s
purported offense, Grigg contends that the district court erred
by not adequately considering the harmlessness of the misde-
meanor noise violation and that Hensley should not have been
extended to validate the Terry stop here. The government
counters that Hensley need not be limited to completed felo-
nies because the interest in locating suspects of past misde-
meanors remains of importance in this case and others. Under
this interpretation, the government argues that the actions of
Officers McGuire and Roeder were constitutional because an
investigatory stop of Grigg to identify him as the driver of the
Cougar and inquire about his side of the story was, under the
circumstances, the best approach to resolve the noise com-
plaint, and thus reasonable under the Fourth Amendment.

  [2] Whatever may be the conclusion of the analysis, there
can be little doubt that the Supreme Court’s methodology in
Hensley applies to the circumstances here where the Nampa
police officers undertook an investigative stop to determine
                        UNITED STATES v. GRIGG                       10257
whether Grigg was involved in the past noise violation
alleged in Harmel’s complaint. See In re Stern, 

, 1043 (9th Cir. 2003) (“[W]e are bound not only by the
holdings of [Supreme Court] decisions but also by their mode
of analysis.”) (internal quotations omitted; second brackets
added by Stern). The facts of Hensley, however, can be distin-
guished because that case concerned a completed felony of
armed robbery, whereas Grigg’s excessively loud music argu-
ably resulted at most in a misdemeanor violation of the local
noise ordinance that does not endanger the public.5 See Gad-
dis v. Redford Twp., 

, 771 n.6 (6th Cir. 2004)
(“Police may . . . make a stop when they have reasonable sus-
picion of a completed felony, though not of a mere completed
misdemeanor.”) In Hensley, the Supreme Court pointed out
the obvious and patent public safety risk in allowing a suspect
of armed robbery to remain at large. 

. This
potential threat of violence created the exigency in Hensley to
stop the suspect that justified foregoing the Fourth Amend-
ment’s warrant requirement. See 

the con-
text of felonies or crimes involving a threat to public safety,
it is in the public interest that the crime be solved and the sus-
pect detained as promptly as possible.”). In sharp contrast, it
is difficult to imagine a less threatening offense than playing
one’s car stereo at an excessive volume. The absence of any
danger to any person arising from the misdemeanor noise vio-
lation here does not support detaining the suspect as promptly
as possible.
  5
    Although the parties and the district court assumed that Grigg’s playing
of excessively loud music, if true, would have been a misdemeanor viola-
tion, the parties do not specify which state or local ordinance might have
been transgressed. For the purposes of our analysis, we accept the parties’
assumption that a misdemeanor was involved, but we note that Grigg’s
behavior was arguably so mild that possibly only a civil infraction would
have resulted, and not a misdemeanor “crime.” However, if a misdemea-
nor crime it was, the playing of music at excessive volume is surely in a
class of relatively innocuous crime, as public safety is not threatened by
violation.
10258               UNITED STATES v. GRIGG
   [3] Although the Supreme Court did not expressly limit its
holding, the reasoning of Hensley suggests that we may prop-
erly consider the gravity of the offense in balancing the inter-
est of crime prevention and investigation against the interest
in privacy and personal security when a court assesses the rea-
sonableness of a Terry stop. In United States v. Jegede, the
district court recognized the applicability of the Hensley bal-
ancing test that included such a focus on the nature of the
offense, see 

, 708 (D. Md. 2003), where
the facts were to some extent analogous to the circumstances
here. In Jegede, the police had received a telephone complaint
from a car following a taxi that observed the taxi stop and the
driver get out to pull up his pants, which apparently alarmed
the complainant that the driver had been having sex in the
back seat or that there was a woman in the car who might
have been assaulted. 

The police dispatch relayed
the complaint to an officer in the field, mentioning “possible
indecent exposure.” 

officer later pulled over the
taxi driver, who by then was acting lawfully, there was no
sign of another person, but the officer detected signs of intoxi-
cation on the driver and arrested him. 

Noting that
indecent exposure was only a misdemeanor in Maryland, 

the district court held that the stop was unconstitu-
tional because the concern about criminal conduct by the
untrained complainant, filtered through the dispatch, did not
provide a reliable basis for an officer’s reasonable suspicion
to warrant the investigative stop. 

(“Once the offi-
cers located the taxi . . . and saw no dangerous activity, they
could and should have inquired again of the basis for the con-
cern and suspicion of indecent exposure and then made an
evaluation of reasonable suspicion and/or continued to
observe the taxi to see if other suspicious conduct occurred.”)
(emphasis added).

   The court in Jegede perceived that an exigency of danger
must link the past completed misdemeanor conduct to the
officer’s justification to stop a suspect under Hensley. The
district court explained:
                     UNITED STATES v. GRIGG                10259
    It is one thing to uphold a stop on suspicion of a mis-
    demeanor, not committed in an officer’s presence,
    when there is potential for repeated danger, such as
    weaving or other dangerous driving. It is quite
    another to uphold a stop for a completed misdemea-
    nor when there is no indication that it will be
    repeated, or cause danger to others, and particularly
    when the police have the means to identify the
    driver.

(emphasis added). The government is correct that
the Jegede court primarily granted relief to the defendant in
that case because of the unreliability of the complaint, but the
district court nevertheless reasoned that indecent exposure by
its nature has no potential for danger, unlike reckless driving,
which might otherwise countenance a reasonable Terry stop.

   In state court cases addressing the identical or similar fac-
tor, the state courts have split, with the decisive issue being
the dangerous nature of the underlying misdemeanor that gave
rise to the Terry stop. In State v. Duncan, 

, 515,
521 (Wash. 2002) (en banc), the Washington State Supreme
Court held that police could not initiate a Terry stop and frisk
after they observed a suspect who might have committed a
civil infraction (drinking alcohol in public). The Duncan court
acknowledged the principle in Hensley that the traditional
interest in officer safety and crime prevention “may not be
present when dealing with past crime.” 

(“The . . .
focus on preventing crimes, and promoting the interests of
justice in arresting felons in Hensley, suggests that the interest
in preventing civil infractions may not be accorded the same
weight.”). The Washington State Supreme Court also under-
scored the distinction between felonies and misdemeanors
that bears on the delicate balance between public safety and
personal security from governmental intrusion:

    [T]his court has cited favorably the common law rule
    requiring a warrant prior to arresting an individual
10260               UNITED STATES v. GRIGG
    for the commission of a misdemeanor. . . . This rule
    illustrates the higher burden this court imposes upon
    officers when investigating lesser crimes. Accepting
    the presumption that more serious crimes pose a
    greater risk of harm to society, we place an inversely
    proportional burden in relation to the level of the
    violation. Thus, society will tolerate a higher level of
    intrusion for a greater risk and higher crime than it
    would for a lesser crime.

-19 (internal citations omitted).

   Likewise, in Blaisdell v. Comm’r of Public Safety, 

, 881, 883-84 (Minn. Ct. App. 1985), aff’d on
other grounds, 

(Minn. 1986), the Court of
Appeals of Minnesota invalidated the stop of a driver who
was seen committing a “no-pay” theft from a gas station
because it was a misdemeanor that is, by definition, inherently
less severe than a felony. In reaching this decision, the appel-
late court noted

    a legislative recognition that the public concerns
    served by warrantless misdemeanor arrests are in
    some degree outweighed by concerns for personal
    security and liberty. At the very least, because mis-
    demeanor offenses are considered less serious crimes
    than felonies and because police cannot arrest for
    misdemeanors unless the offense is committed in
    their presence, the public concerns served by sei-
    zures to investigate past misdemeanors are less grave
    than the concerns served by seizures to investigate
    past felonies and gross misdemeanors.

reason, the appellate court in Blaisdell imposed a
per se rule in Minnesota that Hensley is inapplicable to past
misdemeanor conduct. 

(“While we can envision
situations where an automobile stop could advance the public
interest to a greater degree than the present stop, we do not
                    UNITED STATES v. GRIGG                10261
believe this will arise in a misdemeanor context with suffi-
cient frequency to appreciably advance the public interest in
solving past crimes.”); see also State v. Bennett, 

, 636 (Fla. Dist. Ct. App. 1988) (affirming trial court’s
holding that investigative stops involving past misdemeanors
are constitutionally impermissible).

   State courts have also applied the Hensley test to completed
misdemeanors and reached the opposite conclusion that the
governmental interest in investigating and preventing lesser
crimes does not unduly infringe on personal security under
the Fourth Amendment. In State v. Myers, a Louisiana appel-
late court considered the applicability of Hensley where the
Louisiana state police stopped the driver of a 1985 gray Lin-
coln Continental believed to have struck a traffic sign across
the border in Arkansas according to a teletype issued by the
Arkansas authorities that gave a matching description of the
car later seen in Louisiana. 

, 701-03 (La. Ct.
App. 1986). Although the car was not driving unlawfully
when it reached Louisiana, 

the appeals court held
that the investigative stop was not unconstitutional in light of
the potential hazards related to the offense:

    We have a scenario apparently involving a driver
    who left the scene of an accident. Damage was
    caused, perhaps intentionally, to government prop-
    erty. At the very least, we are dealing with an
    impaired or non-attentive driver who might have
    been dangerous to other traffic. The safety of the
    motoring public and the potential capacity of the
    automobile to inflict serious damage provides a
    fairly strong government interest.

(distinguishing Blaisdell because of the differing
degrees of potential public harm and the close temporal prox-
imity of the “past” crime of reckless driving compared to the
two-month time lapse after the “no-pay” theft).
10262                  UNITED STATES v. GRIGG
   In City of Devils Lake v. Lawrence, 

, 467,
473 (N.D. 2002), cited by the government here to support the
district court’s ruling, the North Dakota Supreme Court con-
fronted a situation where a police officer responded to a call
from police dispatch that “a fight was going to begin” at a bar
and upon arrival at the scene was told by a witness that the
defendant was the one involved in the “verbal altercation.”
Reversing the grant of the defendant’s motion to suppress, the
North Dakota high court reasoned that

      [a] law enforcement officer could reasonably infer
      and deduce from this dispatch, at the very least, the
      possibility that someone at the bar had engaged in,
      or was engaging in, ‘violent, tumultuous, or threaten-
      ing behavior’ with intent to harass, annoy, or alarm
      another person within the meaning of [the state dis-
      orderly conduct statute], to necessitate a call for
      police assistance.

Although the North Dakota Supreme Court did not
address Hensley explicitly, that court was alert to the potential
threat arising from a suspected past misdemeanor of disor-
derly conduct, which favored permitting the investigatory stop
to quell the possibility of escalating violence.6
  6
    See also State v. Burgess, 

, 1227-28 (Me. 2001)
(upholding stop without mention of Hensley to investigate complaint of
previous threat by drunken man to shoot holes in a vehicle if not moved);
Floyd v. City of Crystal Springs, 

, 117 (Miss. 1999) (hold-
ing, without citation to Hensley, that stop of vehicle reported to have
driven recklessly was constitutional and rejecting “felony/misdemeanor
distinction . . . [that] would require officers to ignore communications of
other officials warning of drivers who may be impaired, ill, reckless, or
dangerous to the public”); State v. Blankenship, 

, 357
(Tenn. Crim. App. 1988) (holding stop constitutional on report that sus-
pect was involved in hit-and-run accident). Although some of these cases
do not rely on Hensley, the common rationale to justify the investigative
stop of an already completed misdemeanor stems from the exigency of
preventing or mitigating public safety risks associated with the nature of
the offense.
                        UNITED STATES v. GRIGG                       10263
   [4] These state cases are instructive because they illuminate
the rule we derive from Hensley that a court reviewing the
reasonableness of an investigative stop must consider the
nature of the offense, with particular attention to any inherent
threat to public safety associated with the suspected past vio-
lation. A practical concern that increases the law enforcement
interest under Hensley is that an investigating officer might
eliminate any ongoing risk that an offending party might
repeat the completed misdemeanor or that an officer might
stem the potential for escalating violence arising from such
conduct, both of which enhance public safety. Conversely, the
absence of a public safety risk reasonably inferred from an
innocuous past misdemeanor suggests the primacy of a sus-
pect’s Fourth Amendment interest in personal security.

   [5] As a complement to these practical concerns, moreover,
the formal distinction between felonies and misdemeanors
generally followed under state law in prohibiting warrantless
arrests for misdemeanors committed outside the presence of
the officer also informs our inquiry.7 As noted by the court in
Blaisdell, this formal distinction amounts to “a legislative rec-
ognition that the public concerns served by warrantless misde-
meanor arrests are in some degree outweighed by concerns
for personal security and liberty.” 

; see also 

(“Accepting the pre-
sumption that more serious crimes pose a greater risk of harm
to society, we place an inversely proportional burden in rela-
   7
     In all states covered by our circuit, except Hawaii and Oregon, the
respective state legislatures have observed this distinction by promulgating
laws that prohibit an officer, though with some varying exceptions that are
inapplicable here, from arresting a person who commits a misdemeanor
outside of his or her presence. See Alaska Stat. § 12.25.030 (2006); Ariz.
Rev. Stat. Ann. § 13-3883 (2007); Cal. Penal Code § 836 (2007); Idaho
Code Ann. § 19-603 (2007); Mont. Code Ann. § 46-6-311 (2005) (allow-
ing for warrantless arrest not in the presence of an officer in the event of
circumstances involving violence); Nev. Rev. Stat. Ann. § 171.124 (2007)
(allowing for arrest for gross misdemeanor committed outside officer’s
presence); Wash. Rev. Code Ann. § 10.31.100 (2007).
10264                   UNITED STATES v. GRIGG
tion to the level of the violation.”). In light of this distinction,
our evaluation of a Terry stop in the context of a completed
misdemeanor should tend to give primary weight to a sus-
pect’s interests in personal security, while considering the law
enforcement’s interest in the immediate detention of a suspect
is not paramount. Although federal constitutional law is con-
trolling, we note this formal distinction under state law
because “[s]tate law is often relevant in analyzing the reason-
ableness of police activities under the fourth amendment.”
Reed v. Hoy, 

, 325, 330 & n.5 (9th Cir. 1990)
(examining reasonableness in context of § 1983 and claim of
qualified immunity); see also Bingham v. City of Manhattan
Beach, 

, 950 (9th Cir. 2003) (“In evaluating a
custodial arrest executed by state officials, federal courts must
determine the reasonableness of the arrest in reference to state
law governing the arrest.” (internal quotation marks and alter-
ation omitted)).8
  8
    Consideration of the nature of the offense under Hensley is also consis-
tent with the Fourth Amendment reasonableness inquiry in the context of
a warrantless entry into a home of a person suspected of a non-jailable
traffic offense. See Welsh v. Wisconsin, 

, 750 (1984). In
Welsh, the arrest occurred after a witness observed a car swerve into an
open field and called the police. 

When the witness told the
police that the car’s driver walked away from the accident, the police
checked the car’s registration, determined that Welsh lived nearby, and
presently gained entry to his house without a warrant and arrested him for
driving while intoxicated. 

government’s exigency theo-
ries, the Supreme Court invalidated the entry and arrest in light of the
minor nature of the offense. 

750 (“Our hesitation in finding
exigent circumstances . . . is particularly appropriate when the underlying
offense for which there is probable cause to arrest is relatively minor.”);
accord United States v. Johnson, 

, 908 (9th Cir. 2001) (en
banc) (recognizing that where the police are in hot pursuit of defendant
who has committed the misdemeanor of resisting arrest, the relatively
minor nature of the offense “weighs heavily against” the reasonableness
of a warrantless entry onto a suspect’s property based on exigent circum-
stances). Doubtless, a Terry stop is less intrusive on personal security than
the home entry in Welsh; however, that distinction does not detract from
the Fourth Amendment command common to both settings that individual
privacy must be protected from unreasonable encroachment where the
defendant has committed a mere misdemeanor. See Johnson, 256 F.3d at
                      UNITED STATES v. GRIGG                     10265
   [6] Despite the misdemeanor-felony distinction, and the
fact that some courts have relied on this distinction to limit
Hensley, we decline to adopt a per se standard that police may
not conduct a Terry stop to investigate a person in connection
with a past completed misdemeanor simply because of the
formal classification of the offense. We think it depends on
the nature of the misdemeanor. Circumstances may arise
where the police have reasonable suspicion to believe that a
person is wanted in connection with a past misdemeanor that
the police may reasonably consider to be a threat to public
safety. See, e.g., 

(reckless driving),
Devils 

(altercation with a potential
for violent escalation); 

(drunken
person making threats that he would shoot vehicle if not
moved). We leave that case for another day.

   [7] We adopt the rule that a reviewing court must consider
the nature of the misdemeanor offense in question, with par-
ticular attention to the potential for ongoing or repeated dan-
ger (e.g., drunken and/or reckless driving), and any risk of
escalation (e.g., disorderly conduct, assault, domestic vio-
lence). An assessment of the “public safety” factor should be
considered within the totality of the circumstances, when bal-
ancing the privacy interests at stake against the efficacy of a
Terry stop, along with the possibility that the police may have
alternative means to identify the suspect or achieve the inves-
tigative purpose of the stop.

                                   B

  [8] We conclude that Officers Roeder’s and McGuire’s
investigatory stop of Grigg was not reasonable. As discussed
above, the exceedingly harmless past misdemeanor conduct

908 n.6. (“[I]n situations where the underlying offense is only a misde-
meanor, law enforcement must yield to the Fourth Amendment in all but
the ‘rarest’ cases.” (quoting 

)).
10266               UNITED STATES v. GRIGG
— allegedly playing one’s car stereo at a volume in suspected
violation of a local noise ordinance — need not spur the
police into instant action as might the opportunity to stop a
reputedly armed felon, street fighter, or reckless driver. Cf.

; Devils 

;

. So far as we can discern, if Officers
McGuire and Roeder had not stopped Grigg, the threat to pub-
lic safety from his loud music would have been nil. Given the
lack of exigency to seize Grigg temporarily, his interest in
personal security against governmental intrusion is entitled to
more deference.

   Moreover, the countervailing strength of the governmental
interest in crime prevention must be gauged in light of the
alternative methods the Nampa police had to ascertain Grigg’s
identity. The district court made findings with respect to two
alternative means of identifying Grigg. First, the district court
determined that it would have been unreliable for Officer
McGuire to have dispatch check the complaint logs. In addi-
tion, the district court found that the length of time required
to have dispatch check the logs would have permitted Grigg
to leave the area. This finding appears to us to be correct
because a check of the complaint logs would have been inef-
fective where Harmel did not know Grigg’s identity and he
could thus not have provided it in a previous complaint.

   [9] The district court’s second finding that Officers
McGuire and Roeder could not have retrieved reliable infor-
mation about the driver of the Cougar from the residence at
1800 East Dewey Street, however, is less tenable. The district
court found that this method was unreliable because the offi-
cers could not have known whether anyone was home at the
residence; and if someone were home, whether the resident
would have provided the information sought because that per-
son would have been under no duty to do so. Although the
possibility of non-cooperation existed, it was too speculative
to support the district court’s finding, where there was at least
a reasonable probability that a resident would have given the
                       UNITED STATES v. GRIGG                       10267
information upon police inquiry. We may not lightly assume
that members of the public will necessarily be uncooperative.
There was no reason here to assume that police questioning
of the neighbors about a noisy car would have met a stone
wall. The Nampa police took no steps to pursue these oppor-
tunities to investigate the noise complaint, although they
might have been equally fruitful as directly pulling over
Grigg. That Grigg was leaving the area, on which the district
court relied to support its reasoning, has relatively minimal
force because of the innocuous nature of the offense and the
possibility that the driver could be identified by further inves-
tigation. Moreover, the district court’s finding of unreliability
is not entirely supported by the record because Officer
McGuire testified that absent the opportunity to stop Grigg
directly, and in lieu of the ineffective method of checking the
complaint logs, “it would have been quicker for me to just go
down to the address where he came from and ask them for the
name of the individual that had just left. I would have proba-
bly investigated it that way.” There was no testimony that
Officers McGuire and Roeder lacked confidence that contact
with the residents at 1800 East Dewey Street would have pro-
duced Grigg’s identity. Finally, the district court’s speculation
that the residents might not have been home is not a powerful
ground for an immediate stop of the car because Grigg had
left the residence only moments before the stop, and even if
the residents were away temporarily, the police could have
returned to question them.

   [10] That the police failed to run a routine license check on
the Cougar compounds the unreasonableness of the stop. On
this point, the district court made no finding, although Officer
Roeder was in a position, as he trailed Grigg before pulling
him over, to run a check on the license plate that would have
accessed solid information on the Cougar and the registered
owner.9 While it is possible that Grigg might have borrowed
  9
   We have recently held that “when police officers see a license plate in
plain view, and then use that plate to access additional non-private infor-
mation about the car and its owner, they do not conduct a Fourth Amend-
ment search.” United States v. Diaz-Castaneda, No. 06-30047, 

at *4 (9th Cir. July 18, 2007).
10268               UNITED STATES v. GRIGG
the car from the owner, a police officer’s license plate check
is a standard procedure for gathering information about a sus-
pected violation of the law that went untested here.

   This case is nonetheless difficult because we recognize that
the police have a manifest interest in identifying the perpetra-
tors of crime, whether the offense be minor or major. Finding
the violator of even a humble noise ordinance has some value
to society and certainly would have rewarded the persistent
concern of the complaining neighbor Harmel. But giving sat-
isfaction to Mr. Harmel and locating the source of annoyingly
loud music are not all that guide us. There is a traditional and
constitutionally preserved interest in personal security from
governmental intrusion, which fuels the requirements that the
police obtain warrants before making an arrest and that police
have reasonable suspicion that criminal activity is afoot
before making a Terry stop. The matter, in our view, stands
on different footing with regard to a completed crime that is
a misdemeanor that does not endanger the public.

   Directly pulling over the driver of the Cougar was indeed
the most efficient approach to investigating Harmel’s com-
plaint. But simple efficiency and expediency of law enforce-
ment efforts do not automatically override the other crucial
element of the Hensley balancing test — personal security
from governmental intrusion in the operation of one’s vehicle.
See 

(“[T]he reasonableness
of such seizures depends on a balance between the public
interest and the individual’s right to personal security free
from arbitrary interference by law officers.”); see also 

(noting vehicle stops “interfere with freedom
of movement, are inconvenient,[ ]consume time . . . [and]
may create substantial anxiety”). Moreover, the reasonable-
ness of an investigative stop is to a degree undermined,
where, as here, the police have not pursued alternate available
opportunities to gather information about the driver. That
Grigg was leaving the area might have warranted an immedi-
ate Terry stop at the expense of alternative investigative meth-
                      UNITED STATES v. GRIGG                  10269
ods in circumstances involving an offense that threatened
public safety, but the noise violation here created no such exi-
gency. To validate the investigative stop under these circum-
stances would invite the erosion of the Fourth Amendment
rights of Grigg and others.

                                IV

   [11] We hold that under the balancing test set forth in Hen-
sley, a court reviewing the reasonableness of a stop to investi-
gate a past misdemeanor (or other minor infraction) must
assess the potential risk to public safety associated with the
nature of the offense. Under the circumstances here, it was
unreasonable for the Nampa police to pull over Grigg on sus-
picion of having played his music too loudly where they did
not duly consider the lack of any threat to public safety, espe-
cially given the untested alternative means of ascertaining
Grigg’s identity. The motion to suppress was erroneously
denied.10 We reverse Grigg’s conviction and remand to the
district court for further proceedings consistent with this opin-
ion.

  REVERSED AND REMANDED.




  10
    Because we vacate the conviction and remand on this ground, we do
not reach Grigg’s claims of prosecutorial misconduct.