November 3, 2026 | Arizona DUI Defense
Imagine you're serving on a jury in a DUI case. The prosecution presents blood-alcohol test results, and you're supposed to decide whether those results help prove the defendant is guilty beyond a reasonable doubt.
But you have a question: How accurate are these tests?
You ask about the margin of error. You want to understand how reliable the numbers really are.
And then you're removed from the jury.
That's essentially what happened in a Tucson DUI case that made its way to the United States Court of Appeals for the Ninth Circuit.
On November 2, 2026, the court issued its decision in Valle v. Mayes, No. 25-4650. Although the defendant ultimately lost his appeal, the case raises some fascinating questions about DUI blood testing, the role of jurors, and what it really means to prove a criminal charge beyond a reasonable doubt.
As a Tucson DUI defense attorney and former law professor, I find this case particularly interesting because it involves something I think is fundamental to our criminal justice system: the right to question the evidence.
What happened in the Tucson DUI trial?
Michael Valle was charged with two misdemeanor DUI offenses under Arizona law. His case went to trial in Tucson City Court in August 2021.
During the trial, the prosecution presented blood-alcohol testing evidence.
One of the jurors had a concern.
He wanted to know about the standard deviation of the breath and blood tests. If you're not familiar with that term, standard deviation is a statistical measure that can help describe how much results vary.
In everyday language, the juror wanted to know how accurate the tests were.
He submitted a written question to the judge explaining that he was having difficulty reaching a guilty verdict without understanding the accuracy of the testing.
The prosecution became concerned and asked the judge to remove him from the jury.
Here's where things get interesting.
When the judge questioned the juror, he explained that he was a scientist. In his professional experience, understanding the variability of a test was important when evaluating its reliability.
But he also repeatedly told the judge that he could follow the court's instructions, keep an open mind, and wait until all the evidence had been presented.
The judge wasn't convinced.
The juror was removed for cause, meaning the judge determined there was a legal reason he should no longer serve.
The defense objected and requested a mistrial. That request was denied.
The remaining six jurors ultimately convicted Valle of both misdemeanor DUI charges.
How did a misdemeanor DUI case end up in federal court?
This is where the procedural history matters.
Most people understandably assume that when someone appeals a criminal conviction, the appellate court simply decides whether the trial judge made a mistake.
But the process isn't always that straightforward.
After his Tucson City Court conviction, Valle appealed through Arizona's state court system. The state courts rejected his challenge to the juror's removal.
He then filed a federal habeas corpus petition under 28 U.S.C. § 2254.
Habeas corpus is a legal procedure that allows someone to challenge the constitutionality of their custody or conviction after going through the state court process.
The federal district court denied his petition.
Valle appealed again, this time to the Ninth Circuit Court of Appeals.
And here's the crucial distinction: the Ninth Circuit was not simply deciding whether it agreed with the Tucson trial judge.
Because this was a federal habeas case challenging a state conviction, the court had to apply a much more restrictive standard.
Under the Antiterrorism and Effective Death Penalty Act, commonly called AEDPA, federal courts generally cannot overturn a state court decision simply because they believe it was wrong.
The petitioner must satisfy a demanding legal standard involving clearly established United States Supreme Court law.
That's a much harder argument to win.
What did the Ninth Circuit decide?
On November 2, 2026, the Ninth Circuit affirmed the denial of Valle's habeas petition.
In other words, Valle did not obtain relief from his conviction.
But the reasoning is important.
Valle argued that removing the juror violated his Sixth Amendment right to a unanimous jury.
He relied in part on Ramos v. Louisiana, a Supreme Court decision recognizing the constitutional requirement of unanimous guilty verdicts in state criminal jury trials.
The Ninth Circuit explained that Ramos addressed jury unanimity, not the specific question of removing a juror during trial.
Valle also relied on an earlier Ninth Circuit case, United States v. Symington, which addresses concerns about dismissing jurors because of their views on the evidence.
But under the federal habeas standard, Ninth Circuit decisions cannot substitute for clearly established Supreme Court precedent.
The court also declined to consider certain additional arguments because they had not been properly raised in the earlier federal proceedings.
Ultimately, the Ninth Circuit concluded that Valle had not met the demanding standard necessary to obtain federal habeas relief.
That does not mean the court announced a general rule allowing judges to remove jurors whenever they question scientific evidence.
The decision was an unpublished memorandum, meaning it is not binding precedent under Ninth Circuit Rule 36-3, except as that rule permits.
And the court's analysis was shaped by the particular procedural posture of the case.
Why does this matter in Arizona DUI cases?
Let's talk about the bigger issue.
In Arizona, DUI prosecutions frequently involve scientific evidence.
Depending on the case, that might include breath testing, blood testing, toxicology reports, or testimony from forensic analysts.
Those results can be important evidence. But they aren't beyond examination simply because they come from a laboratory or a machine.
A reported blood-alcohol concentration is a measurement. Like other scientific measurements, its significance depends on the testing method, the procedures used, and the circumstances of the case.
That doesn't mean every DUI blood test is unreliable. It means the evidence should be evaluated rather than automatically accepted.
A DUI defense attorney may need to examine how a blood sample was collected, stored, analyzed, and documented. Depending on the circumstances, the attorney may also need to evaluate the laboratory's procedures, quality-control records, or the interpretation of the reported results.
The specific issues vary from case to case.
But here's the point: scientific evidence is still evidence. And evidence can be questioned.
Aren't jurors supposed to question the evidence?
Yes. Jurors are responsible for evaluating the evidence presented at trial.
They must also follow the judge's instructions and decide the case based on the evidence admitted in court.
Those responsibilities generally work together.
The prosecution has the burden of proving every element of a criminal offense beyond a reasonable doubt. The defendant does not have to prove innocence.
A juror may find particular evidence persuasive. Another juror may have questions about its reliability or significance.
The difficult issue in Valle was whether this juror's statements reflected an inability to follow the law or an attempt to evaluate whether the prosecution had met its burden.
The trial judge concluded that the juror should be removed.
The Ninth Circuit later concluded that Valle had not established a basis for federal habeas relief.
Those are related conclusions, but they aren't the same as saying jurors must accept scientific evidence without question.
And that's why I think this case is worth discussing.
What should you do if you're charged with DUI in Tucson?
If you've been arrested for DUI in Tucson or elsewhere in Pima County, don't assume the case is over because the police obtained a blood or breath test.
A DUI investigation involves more than a single number.
The evidence, the testing procedures, the circumstances of the traffic stop, and the applicable Arizona DUI laws all deserve careful review.
Not every case has a viable challenge to the testing evidence. But determining that requires looking at the actual records, not simply accepting the prosecution's summary of what the evidence supposedly establishes.
It's also important to act promptly. Arizona DUI cases can involve separate criminal court proceedings and administrative driver's license consequences, with deadlines that may arise before the criminal case is resolved.
Why I care about this decision
I've spent more than 15 years working in criminal defense, including as a public defender and law professor.
One thing I've learned is that people often assume scientific evidence is more definitive than it actually is.
Sometimes the science is strong. Sometimes there are legitimate questions about the testing process or what the results establish.
The job of a defense attorney isn't to reject science. It's to understand the evidence, identify its strengths and weaknesses, and make sure the prosecution is held to its burden of proof.
That's what makes Valle v. Mayes so interesting.
A juror wanted to understand the accuracy of the DUI testing evidence. His questions ultimately became the subject of years of litigation.
The defendant didn't win his federal appeal.
But the case reminds us why the distinction between questioning evidence and refusing to follow the law matters.
And why a criminal conviction should rest on evidence that has been meaningfully examined.
Charged with DUI in Tucson, Arizona?
If you're facing DUI charges in Tucson, Oro Valley, Marana, Sahuarita, or elsewhere in Pima County, AJB Law Firm provides criminal defense representation focused on protecting your rights and carefully evaluating the evidence against you.
I'm Amanda Bynum, a Tucson criminal defense attorney, former public defender, and former law professor.
If you've been arrested for DUI, contact AJB Law Firm to discuss your case and your options.
Case discussed: Valle v. Mayes, No. 25-4650 (9th Cir. Nov. 2, 2026) (unpublished memorandum).
Read the Ninth Circuit decision.
This article is for general educational purposes and is not legal advice. Every criminal case depends on its particular facts and applicable law.
