What the Body Camera Did Not Record

By Deandra Grant on October 22, 2026

In most Texas DWI cases the body camera video is treated as the referee. The officer says one thing, the defendant remembers another, and everyone turns to the recording to settle it. Clients assume it will exonerate them. Prosecutors assume it will help them convict. Jurors assume it shows what happened.

It shows what entered a lens. A recent piece in Forensic Magazine by Larry Danaher, a former police captain, puts the principle well: accuracy inside the frame is not the same as completeness outside it. The research he points to is worth knowing, and it applies to a roadside sobriety test even more directly than to the use-of-force cases it was written about.

A Chest Camera Is Not the Officer’s Eyes

Start with the physical fact that most people never think about. A body-worn camera is usually mounted on the chest. It points where the torso points. The officer’s observations are made with his eyes, and his eyes move independently of his chest.

Somebody measured the difference. In a 2024 study published in Police Practice and Research, Murray and colleagues put eye-tracking glasses and a chest-mounted camera on 44 active-duty officers running a scripted use-of-force scenario, then compared what the officers looked at against what the camera caught. Officers fixated on 80.5 percent of the critical incidents. The body camera captured 66.2 percent. On the two events that mattered most, the suspect retrieving a weapon and firing it, the officers’ eyes caught 74 and 80 percent while the camera caught 48 and 45.

Two things about that study make it more useful than it first appears. The authors reported that the scenario was deliberately designed so the critical incidents could fall within the camera’s field of view, which means 66.2 percent is a generous number rather than a worst case. And one of the co-authors is William Lewinski of the Force Science Institute, a research organization closely associated with law enforcement. This is not an advocacy finding from the defense bar. It is a police-aligned research group reporting that the camera missed a third of what mattered.

The authors’ own conclusion: viewers may reach different conclusions about an officer’s behavior from the body camera footage than from the officer’s point of view. The gyroscope data told the same story. There was far more head movement than body movement, so the camera’s view simply did not track where the officers were looking.

The Test That Depends on Where He Stood

Now apply that to a DWI stop.

The horizontal gaze nystagmus test is the first of the three standardized field sobriety tests and usually the most heavily weighted by officers. Under the NHTSA manual, the officer holds a stimulus approximately twelve to fifteen inches in front of the subject’s nose, slightly above eye level, and watches the eyes for an involuntary jerking.

So can a chest-mounted camera resolve a small involuntary movement in a person’s eyes? Often, yes. Sometimes, not at all. It is a question rather than a given, and what mostly decides it is how close the officer stood and the angle from a chest mount up to a face. The mistake is assuming the answer in either direction without watching the video closely enough to find out.

That cuts both ways, and the direction people miss is the one that favors the defense. Where the video is good enough to show the eyes, it can contradict the officer: a report claiming six clues against a recording showing smooth pursuit is a cross-examination, not a footnote. Where it is not good enough, the single piece of evidence the State treats as the objective record is silent on the officer’s most important conclusion, and that silence is something to establish on the record rather than assert in argument.

There is a second point buried in that and it is worth making expressly. The manual tells the officer where to stand. If the camera on his chest could not see the subject’s eyes, that is a question about where he positioned himself, and his positioning is itself a compliance issue. And if he was positioned correctly, with the stimulus twelve to fifteen inches from the nose, then the camera on his chest was about as close to those eyes as a camera is going to get.

Here is the useful inversion. Whatever the video shows of the eyes, it is excellent for the administration. The same NHTSA manual requires the stimulus to move at a speed taking approximately two seconds to bring the eye from center to side, at least two complete passes, and a hold at maximum deviation for a minimum of four seconds. Those are timing requirements, and timing is exactly what a video can establish. Count the passes. Time the holds with the timecode. An officer who rushed the test produced clues that the manual says the procedure is not validated to produce, and the video shows you that whether or not it shows you his eyes.

What the Camera Does Badly on the Other Two Tests

The walk-and-turn and the one-leg stand are scored on the feet, and the feet are where the camera is weakest.

Field of view and angle. A chest camera at an angle, often with the officer’s own arm or flashlight in frame, frequently cannot resolve whether a heel touched a toe or a foot came off a line that may not be painted on the road at all.
Lighting and exposure. Roadside stops happen at night in headlights and strobes. Automatic exposure preserves one part of the image by losing another, and the part it loses is usually the dark pavement where the scoring happens.
Wide-angle distortion. These lenses are wide by design. The study above used a 133-degree field of view. Wide angles distort apparent distance and the geometry near the edges of frame, which is where a person taking nine heel-to-toe steps ends up.
Frame timing. Variable frame timing complicates any calculation that depends on elapsed time, and these are timed tests scored on a count. That goes to precision at the margin rather than to the method: a timecode will still establish whether a hold lasted four seconds or two, and whether the officer made two passes or one. Treat it as a limit on how fine a measurement you claim, not as a reason to skip the measurement.

Audio and the Slurred Speech Problem

Audio deserves its own paragraph because slurred speech is in nearly every DWI report and almost nobody challenges the recording of it.

Microphones on a moving scene contend with wind, passing traffic, sirens, and overlapping voices, and automatic gain control continuously adjusts levels in ways that can flatten, distort, or suppress what was said. The Forensic Magazine piece makes a distinction: separate what the microphone recorded, what the officer could actually hear standing there, and what the officer perceived. Those are three different things, and a report that says “slurred speech” collapses them into one.

If there is both an in-car microphone and a body-worn one, get both. They are different distances from the speaker, with different gain behavior, and they will not sound the same.

Slow Motion Changes What Jurors Conclude

Caruso, Burns and Converse published “Slow Motion Increases Perceived Intent” in the Proceedings of the National Academy of Sciences in 2016. Across four experiments with 1,610 participants, using real surveillance footage from a murder and broadcast replays from professional football, viewing an action in slow motion rather than at regular speed caused viewers to perceive it as more intentional. The mechanism was that slow motion made participants feel the actor had more time to act, and the authors found this held even when viewers knew how much clock time had actually elapsed.

In four further experiments with 2,737 participants, showing viewers both the regular-speed and the slow-motion version mitigated the bias but did not eliminate it. The usual fix does not fully work.

A DWI case is not about intent, so do not overclaim the holding. What transfers is the underlying effect: slowed and repeated playback changes how a viewer reads a physical movement, and a three-second stumble examined frame by frame for a jury is not the three-second stumble a person standing on the shoulder saw. Watch the video at normal speed with audio before you form a theory, insist the jury see it that way first, and object when the State’s presentation is built on slowed or looped excerpts.

What This Means in Both Directions

A post like this one can slide into telling defense lawyers to distrust video, which would be bad advice. In most Texas DWI cases the video is the best evidence the defense has. It routinely shows a person walking normally, speaking clearly, and following instructions, while the report describes someone else entirely. That contrast wins cases, and it wins them precisely because juries credit video.

What to Ask For

The original file. What arrives through a district attorney’s download portal is frequently a re-encoded, further compressed derivative. Lossy compression discards information even when ordinary playback looks fine, and the detail it discards is the fine detail you need.
Hash values and the processing record. SWGDE’s best practices for forensic video analysis call for hashing original and working files and documenting processing so another examiner can reproduce the result. Ask for what the State’s analyst did, in a form you could repeat.
Every camera, not the one they chose. Body-worn, in-car, any second officer on scene, and any nearby business or residential camera. Each captures a partial view, and device clocks are often slightly wrong, so ask how they were synchronized.
The activation and buffering record. Ask when the camera was activated, whether the system retains a pre-activation buffer, whether that buffer was preserved, and whether the recording was interrupted at any point.

Our post on how video evidence is enhanced and authenticated covers the forensic side of that work, and our post on deepfake-era evidence covers authentication under Rule 901 when the question is whether a recording is genuine at all. This post assumes it is.

The Bottom Line

A camera records what entered the lens. It does not record everything that entered the event.

None of that makes the video unreliable. It makes it evidence rather than a verdict, and the difference is a question any lawyer can put to a witness: not whether the camera was working, but whether what you say you saw is something this camera, mounted there, pointed that way, in that light, was capable of recording.

If you are facing a Texas DWI built on body camera video, our firm can talk with you about the specific facts.

Deandra Grant is the managing partner of Deandra Grant Law, a Texas DWI and criminal defense firm with offices across Dallas-Fort Worth and Central Texas. She holds a master’s degree in pharmaceutical science and a graduate certificate in forensic toxicology, was the first attorney in Texas to earn the Forensic Sobriety Assessment Certification, and is the author of the Texas DWI Manual.