A DUI file is assembled piece by piece: the reason for the stop, observations, field tests, chemical tests and video. A plain-language look at how each piece fits.
From the outside, a DUI arrest can look like a single moment: blue lights, a roadside conversation, handcuffs. From the inside of a case file, it looks very different. A driving under the influence case is assembled from many separate pieces of evidence, each created at a different moment by a different person or machine, and each with its own strengths and weaknesses. Understanding how those pieces fit together is the first step to understanding how a DUI case is evaluated by prosecutors, defense attorneys and judges.
This article walks through the typical stages of a DUI case and the evidence each stage tends to produce. It is general educational information, not legal advice. DUI law differs from state to state and changes over time, and anyone facing a charge should speak with a licensed attorney in their jurisdiction.
Stage one: the reason for the stop
Most DUI cases begin with a traffic stop, and every traffic stop needs a legal justification. In the United States, an officer generally needs reasonable suspicion that a traffic violation or crime has occurred before pulling a vehicle over. Common reasons cited in DUI reports include weaving within a lane, crossing the center line, speeding, driving unusually slowly, failing to signal, running a light or stop sign, driving without headlights at night and equipment violations such as a broken taillight.
Some cases begin differently: a collision, a call from another driver, a driver found asleep in a parked car or a checkpoint. Each of these starting points creates its own type of evidence and raises its own legal questions.
The reason for the stop matters because if a court finds the stop was not lawful, evidence gathered afterward may be challenged. For that reason, the officer’s written description of the driving and any video showing it are often among the first things reviewed in a DUI file.
Evidence typically created: the officer’s report narrative, dash camera footage of the driving before the stop, dispatch records, and in some cases 911 call recordings or witness statements.
Stage two: initial contact and observations
Once the vehicle is stopped, the officer approaches and begins making observations. DUI reports frequently describe things like the odor of alcohol, bloodshot or watery eyes, slurred speech, fumbling with a license or registration, inconsistent answers and admissions about drinking (“I had two beers”).
These observations are important, but they are also subjective. Bloodshot eyes can result from allergies, fatigue or a long shift. Nervousness can cause fumbling. An odor of alcohol says something about whether alcohol was consumed but little about how much. A careful review compares the written observations with what the video shows and asks whether the descriptions are specific or boilerplate.
Statements made by the driver during this stage can also become evidence. Whether those statements are admissible can depend on whether the person was in custody and whether required warnings were given, which are legal questions for a lawyer and a court.
Evidence typically created: report narrative, body camera audio and video, any notes taken on scene.
Stage three: field sobriety tests
If the officer suspects impairment, they may ask the driver to perform field sobriety tests. The three tests standardized by the National Highway Traffic Safety Administration (NHTSA) are the horizontal gaze nystagmus test, the walk-and-turn test and the one-leg stand test. Officers are trained to give specific instructions and look for specific “clues” during each test.
Because these tests are standardized, how they were administered matters. Were the instructions given correctly? Was the surface level and well lit? Did the driver have medical conditions, injuries, footwear or age-related factors that could affect performance? Was the weather a factor? These questions are often answered, or at least informed, by video.
Field sobriety tests are generally voluntary in many states, though the rules and consequences vary. Anyone wanting to understand their rights in a particular state should consult a local attorney.
Evidence typically created: the officer’s documented clues, video of the tests, training records for the officer.
Stage four: preliminary breath tests
Some officers use a portable breath testing device at the roadside. In many jurisdictions, these preliminary results are treated differently from the evidentiary breath test performed later at a station, and their admissibility at trial may be limited. Rules differ by state.
Evidence typically created: device result, device records.
Stage five: the arrest
If the officer believes there is probable cause that the driver was impaired, the driver is arrested. Probable cause is a higher standard than reasonable suspicion. The arrest decision is typically based on the combination of driving behavior, observations, statements and field test performance, and it can itself be challenged.
Evidence typically created: arrest report, booking records, vehicle tow or inventory records.
Stage six: chemical testing
After arrest, drivers are usually asked to submit to a chemical test of breath, blood or urine. Most states have implied consent laws, which generally mean that by driving on public roads, a person is considered to have agreed to chemical testing under certain conditions, and refusing can carry separate consequences such as license suspension.
Evidentiary breath tests are performed on instruments that must be maintained, calibrated and operated according to specific procedures. Blood tests involve collection, storage, chain of custody and laboratory analysis. Each step creates records, and each record can be reviewed.
Evidence typically created: test results, instrument maintenance and calibration logs, operator certification, observation period records, lab reports, chain of custody forms, implied consent advisement forms.
Stage seven: video recordings
Video is often the most powerful evidence in a DUI case, because it shows what actually happened rather than what someone later described. Dash cameras can show the driving and the roadside tests; body cameras can capture conversations and close-up observations; station cameras can record the breath testing room. Some states, including South Carolina, have statutes addressing video recording in DUI arrests, and whether recording requirements were met can become an issue in a case.
Evidence typically created: dash camera, body camera and station video, metadata and retention records.
Stage eight: the paperwork trail
Beyond the headline evidence, a DUI file contains a long paperwork trail: citations, notices of suspension, bond paperwork, tow records, dispatch logs, CAD reports and more. Inconsistencies between documents, such as times that do not match or descriptions that differ, can matter. A careful review lines everything up on a single timeline.
How the pieces fit together
No single piece of evidence usually decides a DUI case. Instead, prosecutors and defense attorneys look at how the pieces support or contradict one another. Does the video match the report? Do the times line up? Was the breath test instrument in proper working order? Were field tests administered according to training? Were legal requirements followed at each step?
This is the same element-by-element thinking that case preparation tools are designed to support: map each piece of evidence to what it is supposed to prove, then look for gaps and conflicts.
Why both sides review the same evidence
Prosecutors review DUI evidence to decide whether charges are supported and what can be proven. Defense attorneys review the same evidence to identify weaknesses, procedural problems and constitutional issues. Judges and juries ultimately weigh it. Everyone benefits when evidence is complete, accurate and well organized.
A simple DUI evidence checklist
- Reason for the stop, as written and as shown on video
- Officer observations, compared with video
- Driver statements and the circumstances in which they were made
- Field sobriety test instructions, conditions and performance
- Any preliminary breath test result
- Basis for the arrest
- Chemical test results and the records behind them
- Dash, body and station video
- All paperwork and time stamps on one timeline
Common questions
Is video always available?
Not always. Equipment can fail, recordings can be lost, and retention periods vary. Whether video exists, and whether it should, are important questions to ask early.
Can a DUI case proceed without a chemical test?
In many states, yes. Prosecutors may rely on observations, field tests and other evidence, though the strength of such cases varies.
Does a breath test number decide the case?
Not automatically. The reliability of the result depends on the instrument, the procedures followed and other factors that can be examined.
The role of time
Time ties every stage together. The time of driving, the time of the stop, the time of arrest and the time of chemical testing can all matter, particularly where alcohol absorption, observation periods or recording requirements are at issue. Building a single timeline from every document and recording is often one of the most revealing steps in reviewing a DUI file.
When the case is on the Grand Strand
For drivers charged in Myrtle Beach, North Myrtle Beach, Conway, Surfside Beach or elsewhere in Horry and Georgetown counties, South Carolina’s specific statutes, procedures and deadlines apply, and local knowledge of how cases move through the courts can make a real difference. Someone facing a charge in the area may want to speak with Johnny Gardner, a Grand Strand DUI lawyer, who can review the actual evidence in the file and explain how it applies under South Carolina law. Every case is different, and only a lawyer who has reviewed the specifics can give advice about a particular situation.
This article is general educational information about legal processes, not legal advice. DUI laws and procedures vary and change. If you are facing a charge or a license suspension, speak with a licensed South Carolina attorney promptly.