The traffic stop - Law enforcement is required to have reasonable suspicion that a crime has occurred or that a motor vehicle violation has been committed before they are entitled to stop your vehicle. Contrary to popular belief, they may not pull you over "just because they feel like it." If law enforcement cannot appropriately explain their reasons for stopping a vehicle, then all evidence that was obtained following the illegal stop may not be used against you in your DUI case.
Officer investigations - Law enforcement must conduct any investigation in a way that does not infringe upon constitutional safeguards. Therefore, officers may not seize evidence or search your motor vehicle without a warrant, unless an exception to this requirement is present. Law enforcement may not make an arrest without a warrant or without probable cause that a crime has been committed. Police may utilize DUI roadblocks and stop vehicles if they can prove that the roadblock met certain constitutional standards. Evidence that is destroyed, lost, or does not have the proper "chain of custody" information may be cause for a court to dismiss charges or suppress evidence.
Field Sobriety (DUI) Tests - In Pennsylvania, law enforcement will use a variety of Field Sobriety Tests to help them form an opinion as to whether you are intoxicated to a degree that made you incapable of safely driving a motor vehicle. Examples of such tests are the "finger to nose" test, the "one leg stand" test, the "walk and turn" or "heel to toe" test, and the horizontal gaze nystagmus (HGN). Pennsylvania courts have determined that the HGN test and its results cannot be used against a person in trial. There are several factors that may affect performance on these tests, which are arguably difficult to perform while sober. Some of these factors are the condition of the roadway surface, the shoes being worn, the weather or lighting conditions, some medical conditions and some physical injuries.
Video tapes - Some of the law enforcement agencies in Pennsylvania, including the Pennsylvania State Police, are equipped with video equipment in their vehicles that records a traffic stop. The footage will be from a few seconds before they activate their lights and sirens through the end of the traffic stop. Law enforcement is compelled, upon proper request, to turn over these recordings to your attorney. This video may show that police reports are inaccurate, that a person was operating a motor vehicle properly, that the driver did not have problems with speech, balance, and was coherent.
Drug Recognition Evaluations - When law enforcement suspects that a person is under the influence of drugs, but not alcohol, a specially trained police officer is called to make a determination of the person. This officer, a Drug Recognition Expert, will conduct an assessment to determine which drug(s) a person may have in their system. The determination made by this law enforcement officer is clearly subject to human error and should be treated that way.
Implied Consent Warnings - Any individual who is arrested for DUI must be advised of their obligation to provide either a blood, breath, or urine sample to determine the blood-alcohol content (BAC). All persons arrested for DUI must also be advised that there are penalties that will be imposed if they refuse to provide those samples. Therefore, an officer is required to read the proper implied consent warnings in their entirety or charges may be dismissed.
Breath tests - A number of different breath testing devices are used in Pennsylvania including the BAC Datamaster, Intoxilyzer 5000, Intoxilyzer 8000, and Breathalyzer. In order for a breath test sample to be admitted against a person, law enforcement must prove several factors.
The breath test device operator must have been properly trained and certified before administering breath tests. The results cannot be admitted unless the operator has a valid certification.
The breath test device must be inspected on a periodic basis and law enforcement must have documentation showing that the device was in proper working order. These documents must also be provided from one of the approved facilities in Pennsylvania. If those documents are not provided, or if the inspection was not performed within the required time limits, the results may be dismissed.
The breath test operator must follow certain procedures and failure to do so may compromise the results and the results may not be admitted as evidence.
The breath test operator or other law enforcement officer must watch the person giving the samples in order to ensure that those samples are not tainted in any way. They must continue this observation for twenty minutes or the results may be inadmissible.
The sample must be obtained within two hours of the alleged motor vehicle violation or traffic stop. Failure to obtain the sample within two hours may make the results inadmissible.
It is possible for certain medical conditions to affect the results of the breath test. Diabetes can cause a person to show signs or exhibit behaviors that are consistent with intoxication, but are actually diabetic shock. Law enforcement is not usually trained to distinguish between intoxication and diabetic shock. A diabetic attack may also create chemicals that a breath testing machine may misidentify as alcohol and medical reports and expert testimony may prove that a person was not intoxicated but had a medical condition.
Blood tests - When blood samples are taken for testing DUI, law enforcement, hospital personnel, and laboratory technicians have procedures that must be followed to ensure that the samples are not contaminated or compromised in any way.
Law enforcement must show and explain every person who had possession of or came into contact with the sample up until the time of testing. They must also produce scientific materials that may be reviewed by a defense expert to determine if there were any mistakes.
Hospital personnel must also follow certain procedures including ensuring that the needle was properly assembled and inserted in the correct sterilized location of the person, that the collection tubes were not expired or had a faulty seal, that they took an adequate sample that was mixed properly with preservatives and anti-clotting chemicals, and the sample was labeled correctly. These samples must be taken within 2 hours of the stop, accident, or when the police believed this person to be intoxicated.
Samples are then returned to law enforcement who must ensure that the sample was stored properly before being transported for testing.
The laboratory technicians must also follow certain protocols including maintaining the testing devices and testing the sample properly without contaminating the sample.
Police reports - Usually law enforcement will write reports detailing the important events of their investigation and interactions. By law, the prosecution must provide all evidence in its possession, including these reports. Sometimes there are discrepancies in those reports that may lead to the District Attorney's Office dismissing DUI charges, but will at least be used to challenge the officer's recollection of events if needed at trial.