A DWI Prosecution Is Built on Evidence. So is the Defense.

DWI evidence passes through many hands before it reaches a courtroom. It gets collected, handled, tested, and interpreted at every stage of the investigation, and each stage creates its own opportunities for error, procedural failures, and constitutional challenges.

Before prosecutors can rely on a field sobriety exercise, breath test, blood test, or accident reconstruction, law enforcement must first conduct a lawful investigation. That investigation begins before the arrest, often before any test is administered, and sometimes before an officer even approaches a vehicle.

At Denuna & Westbrook, PLLC, we examine how DWI evidence was gathered at every stage, because the reliability of the result depends on the reliability of the process that produced it.

Every Stage of a DWI Investigation Deserves Examination

DWI cases rarely turn on a single piece of evidence. Prosecutors build cases step by step. A traffic stop or welfare check leads to field sobriety testing. Field sobriety testing leads to an arrest. An arrest leads to a breath test, blood draw, or refusal investigation. Chemical testing then becomes the centerpiece of the prosecution.

Each stage depends on the stage before it. A constitutional problem with the initial stop can affect everything that follows. A flaw in field sobriety testing can undermine the probable cause for arrest. A break in the chain of custody can challenge the reliability of a blood result.

Understanding how those stages connect and where the process can go wrong is where effective DWI defense begins.

Video Evidence Has Changed How DWI Cases Are Defended

Years ago, DWI cases depended heavily on an officer’s written report and courtroom testimony. Today, body-camera footage, dash-camera recordings, surveillance video, dispatch audio, and 911 calls provide a better picture of what truly occurred.

Video may confirm an officer’s account. It may also reveal omissions, inconsistencies, problems with field sobriety test administration, or conduct that looks very different from the written report. Because so much of a modern DWI investigation is recorded, video has become one of the most significant sources of evidence in any case and one of the first things we examine.

The Investigation Pages in This Section

Traffic Stops & Welfare Checks

Every DWI investigation has a starting point. Before any other evidence can be used, law enforcement must have a lawful basis for the initial encounter, whether that’s a traffic stop, a welfare check, a citizen report, or an accident investigation. When that basis doesn’t hold up, everything built on top of it can be challenged.

Standardized Field Sobriety Tests

Field sobriety tests don’t measure intoxication. They measure performance on roadside exercises under conditions that affect everyone, intoxicated or not. The research behind these tests was never peer-reviewed, never published in a scientific journal, and produced error rates the lead researcher later acknowledged were unacceptably high. When officers deviate from NHTSA's standardized procedures, the results lose whatever validity they ever had.

DWI Breath Test Cases

The Intoxilyzer 9000 doesn’t directly measure blood alcohol. It estimates a BAC using a fixed mathematical assumption called the partition ratio, a fixed ratio applied to every person in every case that varies significantly from person to person. Calibration records, operator certification, the 15-minute observation period, mouth alcohol, and radio frequency interference all affect whether a result is reliable.

DWI Blood Test Cases

Blood evidence passes through multiple hands and multiple processes before it reaches a courtroom. Collection procedures, chain of custody, laboratory analysis, gas chromatography methodology, and the timing of the draw all create issues that don't appear on the surface of a laboratory report. Hospital blood draws present a unique issue: hospitals test serum, not whole blood, and serum results run 16 to 25 percent higher than a true whole blood BAC. Chris Denuna holds the ACS Forensic Lawyer-Scientist designation with hands-on training through Axion Analytical Labs, giving Denuna & Westbrook the scientific foundation to examine what produced the result, not just what it says.

DWI Refusal Cases

Refusing a chemical test is not an admission of guilt. It creates consequences, including an ALR suspension and the use of refusal evidence at trial, but also creates defense opportunities. In most Texas counties, a refusal now triggers a blood warrant as a matter of routine. When blood is obtained through a warrant, the warrant itself becomes one of the most significant defense issues in the case.

DWI Accidents & Injuries

A DWI arrest involving an accident is more complicated than a routine traffic stop case, not because the legal standard changes, but because the case has more moving parts. Restitution, plea negotiation complexity, nondisclosure ineligibility, and stricter bond conditions all come into play. When serious bodily injury or a fatality is involved, the charge may escalate to a felony with a demanding causation burden.

Scientific Evidence Is Not Beyond Challenge

Modern DWI prosecutions lean heavily on scientific evidence. Blood tests, breath tests, toxicology reports, and laboratory analysis get presented to juries as objective, precise, and conclusive. But that’s not always what the evidence shows.

Laboratories are run by people who make mistakes. Machines require maintenance, calibration, and proper operation. Every chemical test result is built on mathematical assumptions that may not reflect the individual sitting at the defense table. Procedures exist for a reason, and when they aren’t followed, the results can’t be trusted.

A number on a report is not the same thing as proof. Whether the science behind that number actually supports a conviction is what the defense examines in every case.

Contact a Houston DWI Defense Lawyer Today

Understanding how the evidence was gathered is the starting point for evaluating the strength of the State’s case.

Denuna & Westbrook, PLLC represents individuals facing DWI charges throughout Houston and the Gulf Coast region, including Harris County, Fort Bend County, Montgomery County, Galveston County, Brazoria County, and Waller County.