Arizona's high court has given those charged with drunk driving a new tool to try to defeat charges against them.
In a unanimous ruling Monday, the Arizona Supreme Court said defendants can present evidence to jurors that there are variables among individuals, including body temperature, that make it impossible to precisely convert a breath reading to someone's specific blood-alcohol content. That can be crucial in determining whether a person is legally impaired.
Chief Justice Rebecca Berch, writing for the unanimous court, rejected arguments by the Tucson City Attorney's Office that those variables are legally irrelevant. And defense attorney James Nesci said this provides defendants with the ability to rebut breathalyzer readings.
But Deputy City Attorney Baird Greene said this ruling, coupled with an earlier one on the same case by the Court of Appeals, is not a total loss for prosecutors.
"It clearly establishes that we have the right to pursue motions to preclude what we view as clearly speculative evidence,'' he said. "And that's a tool we totally intend to deploy.''
The case involves Joseph Cooperman, arrested by Tucson police in 2010 on driving while being "impaired to the slightest degree.'' Then based on breath tests, prosecutors added the separate charge of driving with a BAC of at least 0.08, a per-se violation of the law.
Prior to trial, prosecutors sought to block any evidence that what showed up on the breath test might not be accurate. But the judge refused, resulting in an appeal.
Nesci pointed out that state law presumes a BAC reading of zero to 0.049 shows the motorist is not under the influence of alcohol. There is no presumption either way for a reading of 0.05 to 0.079, with a jury able to consider "other competent evidence'' to determine if the person is guilt.
Only at 0.08 and above is someone presumed to be legally intoxicated.
Nesci said defense attorneys always have had the opportunity to rebut the accuracy of the readings. Now that path of attack can include physiological variables.
He cited testimony from a defense expert that hematocrit -- essentially the concentration of red blood cells -- can affect blood-alcohol concentrations by up to 5 percent, plus or minus. And that same expert said that even a one degree variance in the temperature of a person's breath from the setting on the breathalyzer could mean a difference up to 8 percent in its BAC reading.
There also are arguments that environmental factors and breathing patterns can affect readings.
"My breath might be at 0.90 but I might actually be at 0.70,'' Nesci said, where a jury cannot presume a person was intoxicated. "Or I might actually be at 0.49 and therefore I'm presumed not under the influence.''
The high court, without comment, upheld the appellate court ruling that those variables are relevant to the question of accuracy of breath tests.
Greene, however, said this is not a stay-out-of-jail free card for Cooperman -- whose case now goes back to the trial court -- or any other defendant. He said they cannot simply argue that there are variables and, therefore, the readings are unreliable.
Instead, he reads the ruling to still require a defense attorney to provide specific evidence of how his or her client's physiology differs from the presumptions the machine makes. Otherwise, Greene said, such testimony is little more than "rank speculation'' that would only confuse the jury.
And Greene said without defendant-specific data, prosecutors will try to preclude such testimony at a trial.
Less of a clear win for defense attorneys what the Supreme Court said Monday about whether they can challenge the related issue of what are called "partition ratios.''
That goes to the relationship between alcohol on the breath and a person's presumed BAC level. The Legislature has decided that, as a matter of law, there is a ratio of 2,100 parts of alcohol on the breath to 1 part of alcohol in the blood.
In writing Monday's decision, Berch said defendants cannot challenge the partition ratios to defeat a per-se charge of driving while intoxicated. She said it is within the purview of the Legislature to decide that someone who blows a 0.08 BAC is automatically guilty.
"The only question in a per se case are whether the breath or blood alcohol count is 0.08 or more and whether the reading was obtained within two hours of driving,'' she wrote. "Whether the defendant was impaired is not at issue.''
But Berch said if prosecutors use breathalyzer readings to try to gain a separate conviction on a charge of driving while impaired, then defendants can argue that the ratios do not apply to their clients.
Greene said prosecutors usually bring both charges -- per se and impaired -- because the Legislature has made that an option. But he said there's also a tactical reason for that.
"Quite frankly, some jurors are more comfortable with scientific-type evidence and they may want to convict on that,'' he said, meaning a specific BAC reading. "Other jurors may be more comfortable with eyewitness evidence of impairment.''
In its Monday ruling, the high court acknowledged arguments by the prosecution that the partition ratios probably underestimate blood-alcohol content. Berch said they are free to make that argument to the jury in any bid to rebut challenges to the accuracy of the readings.