Chemical test results have become a major source of evidence in a DUI trial. Unlike observable traits such as bloodshot eyes, slurred speech and difficulty with balance and movement, breath tests provide hard data.
However, that does not mean that the results are accurate. In fact, a number of factors may skew the results and cause an unfair conviction.
Inadequate operator training
As the AAA DUI Justice Link points out, law enforcement must have training specific to the device before administering a breath test. In Minnesota, the official device is the DataMaster, and the Bureau of Criminal Apprehension trains officers in its use.
The BCA notes that certifications do expire. After successfully passing the written and lab tests, officers must take recertification courses according to the BCA recertification schedule, or they cannot use device results as evidence.
BCA must perform or authorize the maintenance of all DataMaster devices. If unauthorized personnel perform repairs or maintenance, subsequent tests may not be valid. If a device needs repair, operators should take it out of commission immediately.
Common maintenance needs include device recalibration, battery replacement and software updates.
Mouth alcohol and interfering substances
Training materials warn device operation trainees that mouth alcohol could affect the results of the tests. Vomit, belches, alcohol residue in the mouth or products such as medications, cough syrups and breath fresheners can cause a false positive. Gum, candy and tobacco products could also affect the reliability of the results.
According to a KSTP-TV news report, forensic experts have challenged the reliability and accuracy of DataMaster device results. Claims of invalid read-outs include that the device does not reject interceptors that lead to breath alcohol measurement rather than BAC, so the device is measuring the alcohol in the subject’s stomach, instead. Also, research indicates that the devices are rounding some test results up rather than down, as they should be.
The BCA refutes these claims, but the company that produces the devices did not comment. The BCA does not have the source code to verify whether there are software problems.