Problems with the Stop -- Lack of Reasonable Suspicion
Under Fourth Amendment jurisprudence, an officer must have a "reasonable articulable suspicion" before he or she can stop a citizen. Violation of this principle requires that the evidence resulting from the stop be suppressed and that the case be dismissed (if there is insufficient evidence to go forward). There is a body of case law from both state and federal courts that provides guidance as to the appropriate factors an officer may base a stop upon. A mere hunch or general observation is not enough. An officer's observations that can be described as ambiguous will not be enough. Regardless of what factors the officer bases the stop on, the burden is on the government to present this evidence and convince the judge that the totality of the factors amounts to the necessary "reasonable suspicion." Of course, this defense is waived if a proper motion is not made by defense counsel.
Problems with the Arrest -- Lack of Probable Cause
Even if an officer has "reasonable suspicion" to stop a driver, thereafter he must observe sufficient facts to support the existence of probable cause before he can properly arrest the driver for DWI. Upon a proper motion by defense counsel, the prosecutor must present sufficient evidence to the court to establish that the officer had probable cause to arrest. Absent such a showing, the breath certificate and any evidence obtained after the invalid arrest must be suppressed. An officer's probable cause is usually based upon driving behavior prior to the stop (although, there is often no driving behavior observed in many DWI cases), field sobriety testing (see below), a preliminary breath test reading (see below), and the officer's general observations about the driver, such as the driver's demeanor. If the totality of these observations and factors does not amount to probable cause, the evidence obtained after the arrest will be suppressed.
Faulty Application of Field Sobriety Tests
To draw any meaningful conclusions from the results of field sobriety tests administered on the side of the road, an officer must be properly trained in administering the tests and must actually administer the tests correctly. If there is a breakdown in the procedure, the results can be called into question in a DUI / DWI / Drunk Driving / Driving Under the Influence case. The National Highway Traffic Safety Administration (NHTSA), which developed the field sobriety tests currently used, prepared guidelines that govern the administration of field sobriety tests. The guidelines specify the precise manner under which the tests much be given. Absent compliance with these standards, the results of the tests are invalid. Therefore this can be fertile ground for cross-examination at trial.
Challenging the Horizontal Gaze Nystagmus (HGN) Test
The HGN test measures the involuntary jerking of the eye that increases when a person is impaired by alcohol. While it is considered by some to be an accurate test, it is the test most excluded from evidence during hearings and trials. In order to get the results of this test before the judge or jury in a DUI / DWI / Drunk Driving / Driving Under the Influence case, the prosecutor must establish a proper evidentiary foundation for the admissibility of the test. Given the state of the law, and the science underlying the HGN test, it is nearly impossible for a prosecutor to do this without an expert. Testifying officers simply do not have the scientific or medical training and background to provide this foundation. As a prosecutor, I never once encountered a scenario where a judge, when presented with the proper objection and legal argument, allowed an HGN test into evidence. However, the result often came into evidence when attorneys were "asleep at the wheel" or oblivious to the issue
Challenging the Preliminary Breath Test (PBT)
Many times, an officer will offer the driver a preliminary breath test (PBT) on the side of the road before making a decision on whether to arrest for DUI / DWI / Drunk Driving / Driving Under the Influence. The result of this test cannot be used as substantive evidence against the driver in the case, but can be used by the officer to establish probable cause to arrest. However, it is sometimes possible to prevent the prosecution from using the PBT to establish probable cause at trial. PBT devices must be maintained pursuant to the manufacturer's instructions and procedures and must have an error rate less than 10% according to provisions in the Virginia Administrative Code (VAC). There are also additional requirements related to proper use of PBTs in the VAC. However, I have never encountered an officer that was aware of this information because it is something that usually is not asked of them.
Problems with the Official Breath Test Machine
There is a laundry list of potential technical problems with the admissibility of the results from an official breath test conducted at the station or Adult Detention Center. On a not so infrequent basis, machines are repaired or serviced. If this happens, the machine will need to be tested and recertified before results from that machine can be accepted as valid. If not, the results may be inadmissible. The maintenance records from the breath machine should be obtained from the State so that they can be reviewed in every DUI / DWI / Drunk Driving / Driving Under the Influence case. In addition to the maintenance issues, there are a variety of statutory issues that must be complied with before the results of a breath test are admissible. Each of the requirements should be examined in every case.
Blood Test Cases -- Statutory Compliance Issues
Blood test cases are a nightmare for prosecutors and they recognize it. There is a long list of foundational requirements set forth in the Virginia Code that prosecutors must comply with in order to get the results of a blood tested admitted into evidence. The person drawing the blood must of a certain background, the person must be designated by an order of the circuit court (and the prosecutor needs to have this order at trial), and the blood must be drawn, packaged, and processed in a very specific way. Failure on the part of the prosecutor to lay a proper evidentiary foundation in these areas can result in the blood alcohol result not being allowed into evidence -- assuming the defense attorney makes an objection.
Rising Blood Alcohol Level (BAC) Defense
This argument, commonly referred to as the "relation back" or "rising BAC" argument, acknowledges that under Virginia law, the results of a breath test are rebuttable. Through the use of an expert witness, many times it is possible to present evidence that based upon when a person drank, what they drank, what they ate, and when the test was conducted, that their BAC was below the legal limit at the time of driving even though it was above the legal limit when they were tested 2 to 3 hours later. Where applicable, this is a powerful defense.