DUI & Criminal Defense

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Phoenix, AZ 85006

The Definitive Guide to Defeating an Arizona DUI

If you can’t imagine how an Arizona DUI charge could be defeated, a case dismissed or evidence suppressed then you are not alone.  Most jurors (start off) thinking these cases are cut and dry as well.  For that matter, many attorneys don’t have the expertise to identify the makings of a strong defense.  

However, there are people in Arizona who have won a DUI, been found not guilty of vehicular manslaughter and had their evidence suppressed in an Aggravated DUI case.  It happens much more than you might think.  Does it happen to all my clients?  Of course not.  However, it happens…more than it should.  If you have been accused of an impaired driving offense then the information will help you understand how these case can successfully be defended.  If you are a lawyer seeking to help own clients fight a DUI then this page should also provide the necessary strategy and tactics.


There are no DUI cases without forensic evidence.  A result of an alleged scientific test is usually the end-all be-all of the government’s case. Consequently, the ability to challenge this kind of evidence is the primary challenge in just about every DUI or vehicular crimes case.

Blood Tests for Alcohol

Measuring the amount of alcohol in a person’s blood requires a process with lots of rigor.  There are both human parts and machine parts of the process.  Every step in the process must be done correctly.  How do you know if it was?

Accuracy, Reliability and Validy 

Blood test results in DUI cases require proof beyond just a machine’s ability to produce a number.

Blood Draw (Phlebotomy) Problems 

The process of measuring the amount of ethanol in a blood sample has three phases.  First is the pre-analytical phase where blood is drawn from a person, stored and preserved for testing. A material problem occurring in this stage of the process will invalidate any blood test result. 

Arizona DUI Lawyer

Unreliable DUI Calibration

In DUI cases the machine used to measure the amount of alcohol in a blood sample is called a gas chromatograph. The machine does not inherently know how to identify or measure anything – including ethanol.  The machine has to be taught to identify alcohol.  This process is called calibration.  Using reliable calibrators (known amounts of ethanol) is essential to the measurement process.

When the calibrators used to teach the machine lose degrade there is a loss of ethanol.  Now the machine’s virtual measuring stick makes things look bigger than they are in reality.

In DUI cases a gas chromatograph is calibrated using calibrators that are a mixture of ethanol and water.  A crime lab must address the fact that they are attempting to measure the amount of ethanol in a different matrix – blood.  

One issue that is often overlooked is ensuring that the blood sample is allowed to properly warm prior to the measurement process.  Blood samples are stored in a refrigerator to preserve sample integrity.  However, if they are not allowed to reach room temperature before testing the result can be artificially inflated.  

This is how someone who is under the legal limit can get a blood test result above .08; or how a regular DUI falsely becomes a super-extreme DUI.

Contaminated Samples

  • Methanol
  • Acetone
  • Unidentified Peeks
  • Acetaldehyde

Independent Analysis 

  • State Ex Rel. McDougall v. Corcoran (Keene), 153 Ariz. 157, 735 P.2d 767 (1987).

Breath Tests for Alcohol

Arizona uses breath testing devices that indirectly measure the amount of alcohol in your breath. The only brand of instrument approved in Arizona is an Intoxilyzer by CMI, Inc.  The results of these machines have a tremendous amount of uncertainty. 

  • Partition Rations
  • Indirect Measurements
  • Infrared spectroscopy
  • Breath Temperature
  • Hematocrit Radio
  • Frequency Interference
  • Mouth Alcohol
  • Illegal per se offense
  • Calibration Need
  • Non-specific Analysis
  • Interfering Compounds
  • Homeostatic variables
  • Common Sources of Error
  • Henry’s Law
  • Birchfield v. North Dakota, 136 S. Ct. 2160 (2016).

Blood Tests for Drugs 

Did you know that the result of a blood test for a drug – is not capable of determining whether a person was impaired?

Retrograde Extrapolation

Misusing Field Sobriety Tests

The roadside tests (Field Sobriety Tests) that officers make people perform during a DUI investigation are not scientific.  They are not capable of telling you if a person is impaired to drive a car. 

  • Correlation v. Causation
  • National Highway Traffic Safety Association (NHTSA)
  • Nystagmus
  • Gaze-Evoked Nystagmus
  • Horizontal Gaze Nystagmus
  • Walk and Turn Test
  • One Leg Stand
  • Validated v. Standardized
  • Peer Reviewed Published Science

Principles of Forensic Science

  • Quality Assurance
  • Quality Control
  • The Scientific Method

Measurement Uncertainty

Measurements are not true values. The true value of anything you attempt to measure is unknowable.

Measurements are just estimations. Some better than others. This is true whenever a lab measures the amount of alcohol in a blood or breath sample in a DUI case.

  • Metrology
  • Uncertainty Budgets
  • Root Cause Analysis
  • ISO 17025

Right to an Evidentiary Hearing

A person accused of a crime in Arizona is entitled to a hearing to determine issues of material fact, with the right to be present and to subpoena witnesses. See A.R.S. 13-4238 Evidentiary hearing.
“The rules of evidence applicable in criminal proceedings shall apply, except that the defendant may be called to testify at the hearing.” See A.R.S. 13-4238(B).


If you have been arrested for a DUI, Aggravated DUI of Manslaughter in Arizona then you have rights guaranteed by both the United States Constitution and also the Arizona Constitution.  Many times people overlook the rights given under the Arizona Constitution.  These constitutional protections are the basis of any decision by a court to suppress evidence or dismiss a DUI case. 

Illegal Traffic Stops

The police need a reason to pull over your car. How good the reason must be is a complicated question that often has a subjective answer. The law requires that a police officer have reasonable suspicion that a crime was committed to justify a traffic stop.

Illegal Arrests for DUI

To arrest a person for DUI in Arizona the police must have probable cause that you were impaired by alcohol (or a drug).  This usually requires probable cause to believe that your alcohol concentration is above the legal limit.  So, what is required for them to meet this burden?

Illegal Searches in DUI Cases

The Fourth Amendment to Constitution protects people from unreasonable search and seizures by the government.  The Arizona Constitution seems to even go further by giving a right to privacy in your “private affairs.”  What does these right really protect in Arizona DUI cases?

Warrantless Seizure of Blood

A warranted seizure of blood is presumed unconstitutional.  These types of cases have received a lot of attention from Arizona courts in the last couple of years.  There is has been a trend away from allowing warrantless blood draws, but also a tendency towards permitting warrantless breath testing.

  • Missouri v. McNeely (2013)

Challenging Search Warrants

Search warrants for a blood sample based on unreliable or false information.

  • Franks v. Delaware Motions

Right to Counsel in DUI Cases

In Arizona, the Right to Counsel attaches well before it does under the federal law.
Arizona DUI Right to Counsel

  • Choice of counsel
  • Sixth Amendment to the United States Constitution

Exculpatory Evidence Rights 

Arizona is one of the few states that guarantee the right to independent testing of a blood sample.  

Lost or Destroyed Evidence

The government has duty to preserve reasonably accessible evidence having a tendency to exonerate a person. Failure to preserves such evidence can result in a due process violation.

Unreliable Identification in DUI Cases

What evidence proves who was driving the car?  In a common case where a police officer makes the traffic stop this is not an issue.  However, in the situation where the police arrive at the scene of an accident, well after it occurred, many people overlook the problem of identification.

Suggestive Line-Ups

Outrageous Government Conduct in DUI Cases

This is a defense to a criminal allegation due to police conduct “so outrageous” that due process principles would absolutely bar the government from invoking a “judicial process to obtain a conviction.”

Speedy Trial Right Violations in DUI Cases

The right to a speedy trial is actually intended to benefit the accused and the public.  It is primarily intended to ensure that a person is treated fairly.  At the same time, society also has an interest in resolving cases as soon as practicable.

The Right to Confront the Crime Laboratory

  • Confrontation Clause issues


Arizona law makes not just driving, but also being in control of a vehicle that is not moving while impaired, a crime.

No Actual Physical Control

Arizona law considers a variety of factors to if a person as actual physical control of a car.  Some of these factors are:
  • Whether the vehicle was running;
  • Whether the ignition was on;
  • Where the ignition key was located;
  • Where and in what position the driver was found in the vehicle;
  • Whether the person was awake or asleep;
  • Whether the vehicle’s headlights were on;
  • Where the vehicle was stopped…

Car as a Shelter

Arizona case law has reaffirmed that a car may be used as a “shelter” by a person intoxicated without being in actual physical control of the vehicle.  However, there is not a traditional safe harbor defense for relinquishing control after realizing you should not be driving.


What do you do about a claim that is not true?  You show it could not be true…or there is a motive for someone to see what they want to see. 

Arrest Quotas for DUI cases

Best DUI Lawyer Scottsdale

Body Camera Video Audits

Arizona DUI Attorney

Police body camera videos are relatively new in Arizona.  While the Scottsdale Police Department has had them for several years the Phoenix Police Department just started using them in 2019.  However, just reviewing the video that the government has disclosed may not show you everything that was recorded.  To determine if the video is incomplete or edited in a misleading manner you must review the video’s metadata.

Public Records Investigations

Access to public records can be essential to establishing innocence.

There are many instances where courts are reluctant to compel the government to disclose evidence pursuant to the Rules of Criminal Procedure.  However, Arizona’s public record laws are much more robust than the discovery rules.  

Obtaining Police GPS Data

Police GPS Data DUI
Prior Instances of Untruthfulness

Need help?  
Call the Firm directly at (602) 494-3444.