Appellant-Defendant Justin Wells Grigg appeals the district court’s denial of his motion to suppress an unregistered automatic firearm that police officers discovered while conducting an investigative stop of Grigg pursuant to a citizen’s complaint that Grigg had been playing his car stereo at an excessive 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 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 Nam-pa, Idaho had discovered 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 Amendment 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 hearing 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 neighborhood had been harassing him with loud music for “years,” and that he had “caught” the ear 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 testified that he did not know whether the police responded to the previous complaint, according to Officer McGuire’s testimony, 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 Harmel 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 *1073 identity, and serve the driver with a citation and summons. Officer McGuire then completed the complaint form, which Har-mel 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 misdemean- or noise violation because under Idaho law he could not arrest a suspect for a misdemeanor not committed in his presence. 2 Officer McGuire testified that he did not inquire with dispatch to check whether in making the prior complaint Harmel had given the license number of the Cougar. Officer McGuire testified further that under Nampa Police Department 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 subject’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 officers 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 government’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
*1074
completing 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 would have provided probable cause to stop Grigg for a present noise violation. The district court concluded from these findings that Officers McGuire and Roeder conducted an investigative stop under
Terry v. Ohio,
Because the criminal conduct that the officers were investigating had already occurred, the district court held that
United States v. Hensley,
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 knowingly possessing the unregistered SKS automatic rifle. Grigg timely appealed. 3
II
The reasonableness of an investigatory stop is reviewed de novo.
See United States v. $109,179 in U.S. Currency,
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 seizures.” U.S. Const. Amend. IV. Under
Terry
and its progeny, police may, consistent with the Fourth Amendment, stop persons in the absence of probable cause under limited circumstances.
See Dunaway v. New York,
An investigatory stop can be undertaken to prevent ongoing or imminent crime,
i.e.,
when a police officer “observes unusual conduct which leads him reasonably to conclude in light of his experience that criminal activity may be afoot.”
Terry,
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 driver.
Upholding the district court’s denial of Hensley’s motion to suppress the firearm, the Supreme Court employed a balancing 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.”
Id.
at 225, 228,
*1076 A stop to investigate an already completed crime does not necessarily promote the interest of crime prevention as directly as a stop to investigate suspected ongoing criminal activity. Similarly, the exigent 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.
Id.
at 228-29,
Despite these differences, where police have been unable to locate a person suspected of involvement 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 investigation, 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.
Id.
at 229,
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 misdemeanor 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 felonies because the interest in locating suspects of past misdemeanors 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 complaint, and thus reasonable under the Fourth Amendment.
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 whether Grigg was involved in the past noise violation alleged in Harmel’s complaint.
See In re Stem,
Although the Supreme Court did not expressly limit its holding, the reasoning of
Hensley
suggests that we may properly consider the gravity of the offense in balancing the interest of crime prevention and investigation against the interest in privacy and personal security when a court assesses the reasonableness of a
Terry
stop. In
United States v. Jegede,
the district court recognized the applicability of the
Hensley
balancing test that included such a focus on the nature of the offense,
see
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:
It is one thing to uphold a stop on suspicion of a misdemeanor, 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 *1078 completed misdemeanor 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.
Id. at 708 (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 factor, 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,
[T]his court has cited favorably the common law rule requiring a warrant prior to arresting an individual 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.
Id. at 518-19 (internal citations omitted).
Likewise, in
Blaisdell v. Comm’r of Public Safety,
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 misdemeanor 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 seizures to investigate past misdemeanors are less grave than the concerns served by seizures to investigate past felonies and gross misdemeanors.
Id.
For this reason, the appellate court in
Blaisdell
imposed a
per se
rule in Minnesota that
Hensley
is inapplicable to past misdemeanor conduct.
Id.
at 883-84 (“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 believe this will arise in a misdemeanor context with sufficient frequency to appreciably advance the public interest in solving past crimes.”);
see also State v. Bennett,
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 appellate court considered the applicability of
Hensley
where the Louisiana state police stopped the driver of a 1985 gray Lincoln 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.
We have a scenario apparently involving a driver who left the scene of an accident. Damage was caused, perhaps intentionally, to government property. 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.
Id. at 704 (distinguishing Blaisdell because of the differing degrees of potential public harm and the close temporal proximity of the “past” crime of reckless driving compared to the two-month time lapse after the “no-pay” theft).
In
City of Devils Lake v. Lawrence,
[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 threatening behavior’ with intent to harass, annoy, or alarm another person within the meaning of [the state disorderly conduct statute], to necessitate a call for police assistance.
Id. at 473. 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 disorderly conduct, which favored permitting the investigatory stop to quell the possibility of escalating violence. 6
These state cases are instructive because they illuminate the rule we derive *1080 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 violation. 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 suspect’s Fourth Amendment interest in personal security.
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 recognition that the public concerns served by war-rantless misdemeanor arrests are in some degree outweighed by concerns for personal security and liberty.”
Blaisdell,
*1081
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., Myers,
We adopt the rule that a reviewing court must consider the nature of the misdemeanor offense in question, with particular attention to the potential for ongoing or repeated danger {e.g., drunken and/or reckless driving), and any risk of escalation (e.g., disorderly conduct, assault, domestic violence). An assessment of the “public safety” factor should be considered within the totality of the circumstances, when balancing 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 investigative purpose of the stop.
B
We conclude that Officers Roe-der’s and McGuire’s investigatory stop of Grigg was not reasonable. As discussed above, the exceedingly harmless past misdemeanor conduct — 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. Hensley,
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. *1082 First, the district court determined that it would have been unreliable for Officer McGuire to have dispatch check the complaint logs. In addition, 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 ineffective where Harmel did not know Grigg’s identity and he could thus not have provided it in a previous complaint.
The district court’s second finding that Officers McGuire and Roeder could not have retrieved reliable information 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 officers 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 person 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 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 opportunities 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 investigation. 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 probably 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 produced 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.
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 the car from the owner, a police officer’s license plate check is a standard procedure for gathering information about a suspected violation of the law that went untested here.
*1083 This case is nonetheless difficult because we recognize that the police have a manifest interest in identifying the perpetrators 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 satisfaction 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 complaint. But simple efficiency and expediency of law enforcement 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 Brignoni-Ponce,
IV
We hold that under the balancing test set forth in Hensley, a court reviewing the reasonableness of a stop to investigate 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 suspicion of having played his music too loudly where they did not duly consider the lack of any threat to public safety, especially 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 opinion.
REVERSED AND REMANDED.
Notes
. 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.
. 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 public 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....").
. 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.
. Of our sister circuits, only the Sixth Circuit has addressed this issue, stating that the
Hensley
rule did not apply to past completed misdemeanors.
See Gaddis
v.
Redford Twp.,
. Although the parties and the district court assumed that Grigg's playing of excessively *1077 loud music, if true, would have been a misdemeanor violation, 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 misdemeanor 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.
.
See also State v. Burgess,
. 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) (allowing 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).
. Consideration of the nature of the offense under
Hensley
is also consistent 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,
. 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 information about the car and its owner, they do not conduct a Fourth Amendment search.”
United States v. Diaz-Castane
*1083
da,
. Because we vacate the conviction and remand on this ground, we do not reach Grigg’s claims of prosecutorial misconduct.