There are many potential defenses in a DUI case because of the complexity of the offense. The majority can be broken down in the following areas:
Driving. Intoxication is not enough. The Prosecution must prove that the Defendant was driving. This may be difficult if, as in the case of some accidents, there are no witnesses to his being the driver of the vehicle.
Probable cause. Evidence will be suppressed if the officer did not have legal cause to (a) stop, (b) detain and (c) arrest. Sobriety roadblocks present particularly complex issues.
Miranda Warnings. Incriminating statements may be suppressed if warnings were not given at the appropriate time.
Under the Influence. The officer’s observations and opinions as to intoxication can be questioned. An attorney should attack the circumstances of the field sobriety tests and the predisposed nature of what the officer considers “failing”. Other witnesses can also testify that you appeared to be sober.
Blood-alcohol concentration (BAC). There exists a wide range of potential problems with blood, breath or urine testing. Most breath machines will register many chemical compounds found on the human breath as alcohol which can be referred to as a “non-specific” analysis. Also, breath machines assume a 2100-to-1 ratio in converting alcohol in the breath into alcohol in the blood which varies greatly from person to person (and within a person from moment to another). Radio frequency interference can result in inaccurate readings. These and other defects in analysis can be brought out in cross-examination of the state’s expert witness, and/or the defense can hire its own forensic chemist.
Testing during the absorption phase. The blood, breath or urine test will be unreliable if done while you are still actively absorbing alcohol (it takes 30 minutes to three hours to complete absorption). This can be delayed if food is present in the stomach. Thus, having one last quick drink at the bar can cause inaccurate test results.
Retrograde extrapolation. This refers to the requirement that the BAC be “related back” in time from the test to the driving. A number of complex physiological problems are involved here.
Regulation of blood-alcohol testing. The prosecution must prove that the blood, breath or urine test complied with Pennsylvania’s requirements as to calibration and maintenance.