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Science and DUI Testing: The Basics

In January, I posted an article about the importance of knowing your rights during a DUI investigation, specifically your rights when you are initially pulled over, questioned, and asked to submit to field sobriety tests. Your rights as a defendant continue through all of the fact-finding process. Upon arrest your blood, breath, or urine is taken and the samples are sent to a police crime lab for testing. Part of the DUI investigative process includes a more precise scientific determination of your blood alcohol concentration, the results of which could potentially be introduced as evidence during a trial. But what if the machinery that tested your blood isn’t working the way it should?

Most of us assume that crime labs hold these forensic tests to the utmost standards. After all, the results carry significant weight in the courtroom and can affect one’s liberty and reputation. But this is not always the case. Errors can and do occur periodically even with subsequent testing. If there is reason to believe an error has occurred, it is incumbent upon a skilled DUI practitioner to request relevant data and to review it with qualified forensic experts. If you are being charged with a DUI, it is paramount that you consult with counsel that is not only skilled in relevant DUI law but who also places significant emphasis on forensic DUI science and testing procedures. After all, due to the significance of DUI charges, scientifically produced evidence supporting or negating the charge should be subject to strict review. These standards should ideally apply to all evidence in a case.

Your forensic samples are tested on the general assumption that the results will be accurate and trustworthy. But there are many potential sources of error like faulty equipment, analyst error, etc. As such, not every test is performed perfectly so the lab is expected to review all of their results. This is why lab equipment is routinely tested for accuracy, much like you do routine maintenance on your car to keep it running correctly. Labs typically perform Quality Assurance procedures where all of the information produced by a machine is reviewed to determine its accuracy. But mistakes are not always easy to spot; the devil may lie in the details. There may be errors appearing on only some documents that are harder to spot at a glance, that only a trained eye would be able to spot, but can still compromise the integrity of the entire run. A further possibility is that errors may be ignored as well as missed. This is why your attorney should know how to further review these Quality Assurance procedures and not merely take a lab’s stamp of accuracy at face value. If your attorney is familiar with valley and statewide lab testing procedures, he or she will be much more adept at comparing irregularities and standards.

Labs measure accuracy by looking at all of the results from the tests done and making sure they are all acceptable to produce. If a lab mistake is made on a defendant’s sample, then naturally the attorney should be aware of it and able to investigate further. If a machine breaks or malfunctions, which does happen from time to time, then the results from that broken machine aren’t reliable. It would not be logical to use flawed results towards proving an individual’s guilt or innocence. Realistically these ‘bad results’ should not be used at all, but sometimes they are. That’s why it is crucial that you have an attorney with a knowledge of the basic science behind DUI testing procedures, who is able to further investigate any errors made, and is able to work with forensic experts to interpret and understand lab documents. Depending on the information given by the labs, certain conclusions can be drawn about the source of a machine’s error. It’s hard to immediately pinpoint the source of a lab error, especially if you are only looking at some of the documents. If there is a known test error that doesn’t show up on some of the paperwork, it doesn’t mean the error ceases to exist. What it means is that review should be done on all of the paperwork. Savvy legal representation can help to uncover these testing errors, which of course would be relevant to the evidence of a case and potentially relevant to the outcome of a case. Shaky evidence should not be used to convict as this is grossly unjust and violates multiple civil rights. (Refer to my January 12 article for details on recent changes made in Arizona to certain categories of DUI charges and punishments.)

To sum it all up, imagine that you know your bathroom scale is broken. Knowing this, would you still be using it to measure your weight and honestly expect an accurate result? Of course not. The same applies to forensic testing machines, with much more serious consequences.

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