DUI/DWI law varies from one state to the next. And, in most DUI cases, the driver submits to a blood, breath, or urine test as required by implied consent laws. However, in every state, a person can still be prosecuted and convicted for DUI without chemical test results showing the amount of drugs or alcohol in the person's system.
A variety of circumstances lead to the prosecution not having chemical test results in a DUI case. Here are some of the more common scenarios where chemical test results won't be available for a DUI prosecution.
Though the implied consent laws require all drivers who are lawfully arrested for a DUI to submit to chemical testing at the request of an officer, some drivers refuse to do so. An unlawful refusal carries certain consequences (for example, license suspension). But in most situations, drivers who refuse to test can't be forced to do so.
So, when a driver refuses to take an alcohol or a drug test, the prosecution won't have test results to use in the case. However, prosecutors are generally allowed to tell jurors that no test results were available because the driver refused to test. Prosecutors will often argue that the driver refused testing in an effort to hide his or her intoxication.
Another reason that test results of a suspect's bodily fluids may not be available to the prosecutor is because the judge has ruled that the sample collected is inadmissible during trial. This scenario usually results from the suspect's lawyer having successfully argued to the judge that law enforcement violated the suspect's constitutional rights in obtaining a sample of the suspect's bodily fluids. Or the defense attorney may successfully argue that the manner in which the authorities collected the sample did not comply with federal or state procedures.
When a suspect challenges a test's admissibility, a hearing is held before trial without a jury, so the test and the results are not made known to the jury during the suspect's trial if the judge rules that they are not admissible during trial.
It's theoretically possible that equipment failure could hinder law enforcement's ability to get an accurate measurement of the amount of drugs or alcohol in a driver's system. However, equipment failure isn't common, and when it does happen, officers can usually come up with a backup plan. For example, if a breath-test device isn't working properly, the officer can normally request that the driver take a blood test.
In every state, you can be convicted of a DUI based on blood alcohol concentration (BAC) (.08% or more in most states) or actual impairment. A DUI based on BAC is often called a "per se" DUI. To be convicted of a per se DUI, BAC test results are necessary. However, BAC test results aren't to be convicted based on actual impairment.
State laws differ on the level of impairment that prosecutors must prove to get an impairment DUI conviction. Some states require proof that the driver was substantially impaired by drugs or alcohol. In other states, even the slightest degree of impairment is enough for a DUI conviction. There are also a number of states that have standards that fall somewhere between the two extremes.
Whatever the standard, proving impairment generally requires a different type of evidence than that used to prove a driver's BAC. Here are some of the more common ways prosecutors prove driver impairment.
In cases with no BAC test results, the prosecutor will introduce evidence of poor field sobriety test performance. The standardized field sobriety tests—the walk-and-turn, one-legged-stand, and the horizontal-gaze-nystagmus tests—are purportedly reliable tools for determining whether a person is under the influence.
Evidence of field sobriety test performance normally comes in the form of the arresting officer's testimony. The officer's testimony will generally focus on what about the driver's test performance indicated impairment. Sometimes a driver's actions obviously show impairment. But officers are also trained to look for more subtle clues of intoxication that require more explanation for the jurors to understand.
While the prosecutor will likely attempt to convince the jury that the tests are legitimate methods of measuring the defendant's intoxication and that the defendant's performance indicated intoxication, the defendant's lawyer will normally try to undermine the validity of the tests and offer explanations other than intoxication for the defendant's allegedly poor performance on the tests.
In addition to introducing evidence of the field sobriety tests, the prosecutor will often have the officer testify about other observations made of the defendant during the traffic stop and arrest. The officer may describe things like smelling the odor of liquor coming from the defendant's breath, slurred speech, and watery bloodshot eyes. The prosecutor might also have the officer testify to evidence recovered from the defendant's car, such as open beer cans or empty liquor bottles. The officer might also recount how the defendant was driving in a reckless manner, such as swerving, drifting off the road, and the like.
It's becoming fairly common for patrol vehicles to be equipped with dashboard cameras. And many police departments are also requiring officers to wear body cameras. So, in addition to the officer's testimony, prosecutors might introduce video evidence of sobriety test performance and other indications of driver impairment.