Mistake of Law: How to Challenge Your Unlawful Stop

Arizona Court of Appeals: Mistake of Law must be Objectively Reasonable to Avoid Suppression of Evidence obtained after the Stop

Can an Arizona Police Officer’s misreading of a clear and unambiguous law give rise to reasonable suspicion, thereby making a stop lawful?

This was a question for a recent Arizona Appeals Court to decide. In the case, the court considered whether a deputy had reasonable suspicion to stop a driver because the officer thought the rear display light on his vehicle was unlawful.

This article takes a closer look at how defense successfully challenged an unlawful police stop due to the police officer’s mistake of law with these topics:

  • Overview of the case and ruling;
  • Impact of Appeals Court ruling in Arizona;
  • Questions and answers;
  • 11 rights you have at an unlawful stop;
  • 10 good reasons to file a motion to suppress evidence;
  • DUI & Criminal Defense in Phoenix and East Valley AZ


The case arose when two deputies were in a convenience store, and smelled the odor of burnt marijuana near two men.

The police did not stop the men to question them at that point.

The two men left the store without incident and drove away.

The deputies followed the SUV and stopped them several blocks away.

The officers had noticed that a white light was being emitting from the lamp that was shining light on the license plate. At that time, the driver was not given any citations for the lamp.

The officers testified during the suppression hearing, that they thought that the white light seen from a vehicle driving forward violated A.R.S. § 28-931(C) which applies to vehicle lamp colors.

This provision requires that all lighting and reflectors mounted on the rear of any vehicle be red color, except that the light displaying the license plate shall be white.

While the stop was underway, the deputies smelled alcohol and saw that the defendant was flushed and that his eyes were bloodshot.

Officers administered a horizontal gaze nystagmus test, a roadside Standard Field Sobriety Test (SFST).

The results of the SFST suggested that the suspect had been drinking alcohol.

The breathalyzer test measured his blood alcohol content (BAC) at .165, and he was arrested for DUI.

The defendant filed a motion to suppress the DUI test evidence that was obtained during the stop.

The defendant argued that no statute supported the deputies’ claim that white light from a license plate light could contribute to reasonable suspicion to stop a driver.

The prosecution alleged that reasonable suspicion existed because the lamp in question was working properly, but it didn’t have opaque casing and sent out some white light at the back of the SUV.

The trial court did not accept the prosecution’s allegation, and granted the motion to suppress the evidence at the suppression hearing.

Meanwhile the U.S. Supreme Court, ruled on a separate case, involving similar issues.

In Helen v. North Carolina the U.S. Supreme Court decided that a traffic stop did not violate the suspect’s rights because the police officer’s mistake of law was reasonable.

In light of that U.S. Supreme Court Decision, the State decided to file an appeal to the trial court to reconsider suppressing the evidence on the grounds that the deputies had  made a reasonable mistake in the way they interpreted A.R.S. § 28-931(C).

At the reconsideration hearing, the defendant argued that the statute clearly compelled the court to find his lamp wasn’t in violation; the deputies’ interpretation wasn’t objectively reasonable; and that the 4th Amendment of the Constitution provides protection against unreasonable searches and seizure.

At this reconsideration hearing the patrol commander in the same department as the deputies testified, explaining the department’s policy with regard to the rear lighting.

The patrol commander testified that officers were trained to treat rear-facing white lights on vehicles, other than backup lamps, as a violation of § 28-931(C).

Since the officer acted upon his training, the trial court decided to vacate their earlier decision.  They then determined that the officer was reasonable in applying the laws as he understood them.

The defendant moved to request that the trial court reconsider their new ruling, but it was denied.

Upon admittance of the evidence at a bench trial, the defendant was convicted and sentenced for DUI.

The Defendant appealed his conviction to the Arizona Court of Appeals.

The Arizona Court of Appeals reviewed the question of whether an Arizona statute prohibited license plate lamps from emitting white light at the back of a car. If the answer was yes, the deputy had reasonable suspicion to investigate in the defendant’s case.

The Court of Appeals reviewed the Arizona law, which requires lamps to be placed on the vehicle in a manner that illuminates the rear license plate with a white light, making it clearly legible from 50 feet away to the rear.

Another statute provides that lighting devices and reflectors need to glow red, with certain exceptions. One exception is for the light illuminating the license plate, which needs to be white.

The Court determined that the SUV lit up the license plate with a white light as provided under law A.R.S. 28-931 (C) and that the statute was not violated.

The court then looked at whether or not it violated any other Arizona laws.

The court noted that the license plate was working properly; that it made the plate visible from the back of the vehicle; and that it did not create a problem for community welfare or public safety. Therefore, no other laws were broken, and therefore the stop was unlawful.

The court found that the deputy didn’t articulate a legally sound basis for investigating.

But the prosecution argued that the deputy had a reasonable belief that the lamp violated the law.

The court explained that the Fourth Amendment permits only reasonable errors that are objectively reasonable.

One factor the court considered to determine if the mistake of law made by the officer was reasonable, was that the language of the law.  The way the statute was written would have needed to be unclear, or susceptible to multiple interpretations.

The Court of Appeals found that in this case the statute was clear, and unambiguous.  Therefore, it was not objectively reasonable for the deputy to misinterpret it.

Further, the Appeals Court ruled that the fact that the department had trained its officers to misread the law did not render the misreading reasonable.

The Appeals Court vacated the defendant’s conviction and reversed the granting of the prosecution’s motion for reconsideration.

*Note:  The officers did not stop the suspects in this case while at the convenience store when they smelled the burnt marijuana.  But since this incident took place, the Arizona Supreme Court ruled in another case that marijuana is sufficient for probable cause to search.   

Impact of Ruling on Arizona

This case could potentially serve as precedent in cases involving similar questions surrounding Arizona criminal charges.

As of this date, it is not known if the case will be appealed to the U.S. Supreme Court.

It would apply in situations where the police make an unlawful stop if due their incorrect interpretation of law.

If an officer stops a driver believing they are breaking the law, and evidence is obtained which leads to arrest, that evidence may be suppressed if the mistake of law is not objectively reasonable.

It will not be enough for the police to claim they believed the law was violated.   There must be an objectively reasonable basis for it.   One of the grounds for determining if their interpretation of the law was objectively reasonable will be if the law is ambiguous, unclear, or subject to more than one interpretation.

Also, even if the police were trained incorrectly about a non-ambiguous law, that does not justification for concluding that the mistake was objectively reasonable.

In order for police to make a lawful investigative stop, they must still have reasonable suspicion that a violation of Arizona laws has occurred.

11 Rights You Have at an Unlawful Police Stop    

No one is immune from an unlawful stop by police.

If the police believe their stop is lawful, they will likely not change their mind at that time.

Trying to convince them otherwise will only aggravate the situation, which could lead to harm or additional criminal charges.

If you have been stopped by an officer for reasons that you know make the stop unlawful, here are your rights.  Becoming familiar with these rights will help you avoid escalating the situation, or getting additional criminal charges:

  • Remain calm and respectful, and address them as “officer.”
  • You can respectfully disagree for the record, but do so politely; refrain from debating or being argumentative about the reason for the stop.
  • Cooperate with the officer. Provide routine documentation requested such as ID and registration.
  • If you need to reach into your glovebox or elsewhere to retrieve the documents, tell the officer where they can be found and inform them that you will be retrieving from there.
  • Do not volunteer or agree to answer personal questions such as where you’ve been, where you’re going, or what you’ve had to eat or drink that day or evening.
  • Keep your hands on the wheel unless you’ve been instructed otherwise by the officer.  Make sure the officer can see them, if moved elsewhere.  Avoid sudden movements that might be perceived as threatening to the officer.
  • Decline to participate in DUI Field Sobriety Testing. SFSTs are not mandatory. Respectfully let the officer know that it is your understanding that court have held that they can be invalid, and you would not want the results to suggest otherwise.
  • You are within your right to decline a search of your vehicle or belongings unless you’ve been arrested.
  • If the police officer requests a breath or blood test, it is your right to refuse. However understand there will be consequences. By law you will lose your driver’s license for one year. If the officer has probable cause to believe you are impaired and driving under the influence of alcohol or drugs, they will obtain a warrant to get a DUI blood test anyway.
  • If you are arrested be cooperative. At that point the officer has made up his or    her mind, and further objection will only make matters worse.
  • Contact an attorney as soon as reasonably possible following your arrest. If retained, your attorney will file a motion to have any evidence suppressed obtained after the unlawful stop.

Q & A

Q. Do police need have reasonable suspicion to stop me at a DUI Checkpoint?

A. No. Police do not need reasonable suspicion of a crime to make a DUI safety checkpoint stop. Arizona has adopted the NHTSA guidelines which requires only that stops be made in a mathematical order or formula decided in advance by the city and agency.

Q. If police pull me over for a violating a law that I did not realize was a violation, is the stop still legal in Arizona?

A. Yes.  The stop is still lawful. It doesn’t matter if you were unaware for the lawfulness of the conduct, as long as you are aware that the circumstances surrounding the conduct for which you were engaging.

Q. When is an officer’s mistake of law due to misinterpretation considered objectively reasonable?

A. If the officer misinterpreted a law that is genuinely ambiguous, and subject to more than one interpretation.


Q. What if the officer was trained to believe a law applied incorrectly?

A. In this case, the Arizona Court of Appeals determined that an officer’s training, misreading or misapplication of the law due to police procedure, did not make the mistake objectively reasonable.

Q. What happens if police stop me unlawfully, and arrest me based on evidence they gather to use against me.

A.  In that case your attorney can file a motion to suppress the evidence obtained as a result of the unlawful stop. If the court agrees, the evidence can be suppressed and will not be used against you by prosecution.

10 Good Reasons for Defense to file a Motion to Suppress Evidence

When evidence is obtained unlawfully, one remedy for the court is to have the evidence suppressed.   Some reasons to challenge evidence include but are not limited to the following:

  • Evidence obtained in violation of your 4th Amendment rights           or other relevant Constitutional Rights;
  • Evidence that is weak;
  • Tampering of evidence by the police or other third party;
  • A showing that evidence was planted to prosecute the defendant;
  • Lab evidence that is not reliable due to inconsistent results obtained by an independent lab results;
  • Breath evidence that is unreliable due to improper instruction or administration;
  • Field Sobriety Test Evidence that is questionable and invalid based on prior court decisions;
  • Inconsistent or unbiased testimony;
  • Violation of police procedures or protocols in handling, transport or storage;
  • Breath or blood test results that have been contaminated, or have been labeled improperly.

Generally when material evidence is suppressed, it leads to dismissal or acquittal of the charges.The most effective way to challenge the evidence is by retaining an experienced and knowledgeable criminal defense attorney who serves the jurisdiction where you were charged.

DUI & Criminal Defense in Phoenix, and East Valley AZ

Suppression of evidence is only one challenge that can apply when defending criminal charges.

Each case holds a different set of circumstances.  A defense case must be evaluated by an experienced criminal defense attorney who can uniquely tailor your defense strategy.

If you are accused of any type of DUI or drug, or marijuana offenses, in Mesa, Tempe, Chandler, Gilbert, or Scottsdale, consult DUI defense attorney James E. Novak.

James Novak is a DUI & Criminal Defense attorney. He is also a former Maricopa County Prosecutor.

If retained he will gather all evidence available; determine if any of your rights were violated; if there is favorable evidence on your behalf;  and what weaknesses may exist in the evidence or testimony the prosecution plans to use against you.

He will make sure you are treated fairly, and work hard to get the most favorable outcome for your charges.

James Novak provides a free initial consultation for those facing active charges in his service areas.

If you have been charged with a crime call the Law Office of James Novak at (480) 413-1499 and speak directly with Mr. Novak.

Additional Resources:

Other Articles of Interest from our Award Winning Blog:


Contact Information