Former Minnesota Vikings running back Adrian Peterson was recently arrested and charged with two offenses: Driving While Intoxicated (DWI) and Unlawful Carrying of a Weapon. His arrest presents several interesting legal questions and potential defense strategies that are worth examining in detail.
Understanding the Charges Against Adrian Peterson
The DWI Charge: Class B Misdemeanor
Peterson faces a Class B misdemeanor DWI charge. This classification is significant because it indicates this is being prosecuted as a first-offense DWI, despite reports that Peterson may have had a previous DWI allegation. In Texas, a first-offense DWI is a Class B misdemeanor, punishable by up to 180 days in jail and a fine of up to $2,000.
The critical distinction here is between an allegation and a conviction. While Peterson may have been arrested for DWI previously, without a final conviction on his record, the State cannot enhance this charge to a Class A misdemeanor (which would apply to a second DWI). Under Texas law, only a prior final conviction can serve as the basis for enhancement. An arrest, a charge, or even a case that was dismissed or resulted in deferred adjudication does not qualify as a predicate offense for enhancement purposes.
This underscores an important principle in Texas criminal law: you are innocent until proven guilty, and allegations alone cannot be used to enhance subsequent charges.
Unlawful Carrying of a Weapon: Class A Misdemeanor
The second charge Peterson faces is Unlawful Carrying of a Weapon, a Class A misdemeanor under Texas Penal Code Section 46.02.
Unlawful Carrying of a Weapon occurs when a person carries a handgun and is engaged in criminal activity other than a Class C misdemeanor traffic violation. In Peterson’s case, the allegation is that he was in possession of a firearm while allegedly committing the offense of DWI.
As a Class A misdemeanor, this charge carries more serious penalties than the DWI itself: up to one year in jail and a fine of up to $4,000. However, the unlawful carry charge is entirely dependent on the underlying DWI. If the DWI charge cannot be proven beyond a reasonable doubt, the unlawful carry charge fails as well, since there would be no “criminal activity” that makes the carrying unlawful.
How to Defend DWI Charges in Texas
A successful DWI defense requires examining every stage of the investigation, from the moment law enforcement initiated contact through the final chemical testing. Each phase presents opportunities to challenge the State’s case.
Phase One: The Traffic Stop – Was There Reasonable Suspicion?
Before examining the evidence of intoxication, we must first determine whether the officer had reasonable suspicion to initiate the traffic stop. Under the Fourth Amendment, an officer must have specific, articulable facts that reasonably suggest a person is violating the law.
Common issues that can invalidate a DWI stop include:
- The alleged traffic violation did not actually occur
- The driving behavior, while unusual, does not suggest intoxication or a traffic violation
- The officer lacked personal observation and relied on unreliable information
If the initial stop was unlawful, all evidence obtained as a result of that stop—including field sobriety tests, statements, and chemical specimens—must be suppressed under the exclusionary rule. This would effectively end the State’s case.
Phase Two: The Arrest – Was there Probable Cause?
Even if the initial stop was lawful, officers frequently make critical errors in developing probable cause for a DWI arrest. Probable cause requires more than mere suspicion; there must be facts and circumstances that would lead a reasonable person to believe the suspect was driving while intoxicated.
Mistakes in Developing Probable Cause
Officers commonly make these mistakes during the investigation that leads to arrest:
Officers are trained to look for indicators like bloodshot eyes, but they often fail to consider alternative explanations such as fatigue, allergies, contact lenses, or environmental factors. The odor of alcohol establishes only that someone has been drinking, not that they are intoxicated. As a general premise, nervousness during a traffic stop is a natural reaction, not evidence of impairment.
Difficulty retrieving documents from a wallet, fumbling with a seatbelt, or taking time to pull over safely are often cited as indicators of impairment. In reality, these behaviors are common among completely sober drivers who are nervous or unfamiliar with where documents are located in their vehicle.
Some officers decide a driver is intoxicated before administering field sobriety tests, then conduct the tests merely to justify an arrest already made in their mind. This confirmation bias leads them to interpret ambiguous performance as failure.
Field Sobriety Tests: The Cornerstone of Probable Cause
Field sobriety tests are often the primary basis for establishing probable cause to arrest. However, these tests are only reliable when administered according to standardized protocols established by the National Highway Traffic Safety Administration (NHTSA). Officers frequently deviate from these protocols, rendering the results unreliable or inadmissible.
Errors in Horizontal Gaze Nystagmus (HGN) Testing
The Horizontal Gaze Nystagmus test measures an involuntary eye movement. While considered the most reliable field sobriety test, its accuracy depends entirely on proper administration.
The stimulus (usually a pen or penlight) must be held at the correct distance (12-15 inches from the subject’s nose) and moved at the correct speed. Moving too fast or too slow affects the test’s validity. The stimulus must also contrast with the background; testing in poor lighting or with a black pen against dark clothing invalidates results.
Before scoring clues, the officer must verify that both eyes track equally and that the individual can follow the stimulus with their eyes. Failure to do this preliminary check can lead to incorrectly attributing medical conditions or neurological issues to alcohol consumption.
Officers should check for nystagmus at the resting position (eyes forward) before beginning the test. Resting nystagmus indicates a medical condition, not intoxication, and should result in discontinuing the HGN test.
To check for onset of nystagmus prior to 45 degrees, officers must accurately estimate maximum deviation (as far as the eye can go to the side). Many officers incorrectly estimate this angle, leading to false positives.
HGN testing conducted near flashing lights (police car lights), on an uneven surface, or in high winds can produce inaccurate results. The test should be conducted in a controlled environment away from visual distractions.
Numerous medical conditions can cause nystagmus that has nothing to do with alcohol, including inner ear problems, certain medications, brain injuries, and neurological conditions. Officers often fail to inquire about these conditions before attributing nystagmus to alcohol.
Errors in Walk-and-Turn (WAT) Test Administration
The Walk-and-Turn test is a divided attention test requiring the subject to listen to instructions while maintaining balance, then walk heel-to-toe along a line. The standardized scoring identifies eight possible clues of impairment, with two or more clues indicating a failure.
Officers must give instructions in a specific sequence: demonstrate the starting position, explain that the subject must stay in that position until instructed to begin, explain all the walk phase instructions, then ask if the subject understands before saying “begin.” Skipping steps or giving instructions out of order invalidates the test.
Officers should demonstrate the heel-to-toe walk so subjects understand the required movement. Officers who do not routinely make DWI arrests often demonstrate the test improperly. An arrest during the daytime has less of a chance of having a specialized DWI officer make the scene.
Officers often confuse “losing balance during instructions” with simply swaying (which is normal) or score someone for “stepping off the line” when their foot was only partially off. Each clue has specific criteria that must be met; vague or incorrect application of clues invalidates the test results.
Age, weight, injuries, medical conditions, and physical fitness all affect balance and coordination. Someone over 65, more than 50 pounds overweight, or with back, leg, or foot injuries cannot reliably perform this test. NHTSA guidelines specifically note these limitations, but officers often ignore them.
Errors in One-Leg Stand (OLS) Test Administration
The One-Leg Stand requires the subject to stand on one foot with the other foot elevated approximately six inches off the ground while counting aloud for 30 seconds. Four clues indicate impairment: swaying, using arms for balance, hopping, and putting the foot down.
Officers must clearly explain and demonstrate the starting position, specify which foot to raise, explain the counting method (one thousand one, one thousand two, etc.), and tell the subject to keep their arms at their sides. Incomplete instructions lead to performance issues unrelated to impairment.
Some degree of swaying is normal when standing on one leg. Only pronounced swaying (enough that the person appears they might fall) should be scored as a clue. Officers often score minimal, normal compensatory movements as impairment.
The OLS is even more affected by age, weight, and physical condition than the Walk-and-Turn. NHTSA recommends against administering this test to people over 65, those with back or leg injuries, or those more than 50 pounds overweight. Inner ear problems and other balance disorders also make this test inappropriate.
Officers sometimes score difficulty counting as impairment when it’s actually nervousness or confusion about the instructions. The test measures balance and divided attention, not mathematical ability.
How Field Sobriety Test Errors Undermine Probable Cause
When field sobriety tests are improperly administered, they may fail to establish the probable cause necessary for a lawful arrest. An experienced DWI defense attorney can challenge probable cause on multiple grounds:
Suppression of Evidence
If tests were conducted in violation of standardized procedures, a motion to suppress can prevent the jury from hearing about the test results at all. When an officer deviates substantially from NHTSA protocols, the tests lose their scientific reliability and may be excluded from evidence.
Credibility Attacks
Even if test results are admitted, demonstrating that an officer failed to follow proper procedures undermines their credibility. If the jury sees video evidence contradicting the officer’s report or showing improper test administration, they may doubt the officer’s other observations and conclusions.
Expert Testimony
Defense experts can testify about proper SFST administration and point out specific deviations from protocol in the defendant’s case. This expert testimony can be devastating to the State’s case, particularly when supported by video evidence showing improper test administration.
Phase Three: Chemical Testing
One of the most important questions in Peterson’s case is whether officers obtained a chemical specimen—either blood or breath. This detail has not been publicly disclosed, but it fundamentally shapes the defense strategy and the State’s ability to prove intoxication.
The State’s Case With a Chemical Sample
If law enforcement secured a blood or breath sample showing a BAC at or above 0.08, the State can attempt to prove intoxication under the “per se” definition—having an alcohol concentration of 0.08 or more. This is generally considered the strongest form of DWI prosecution because it provides an objective measurement rather than relying solely on subjective observations.
However, even chemical test results can be challenged on numerous grounds, including chain of custody issues, equipment calibration and maintenance problems, testing procedure violations, and the critical issue of retrograde extrapolation.
The State’s Case Without a Chemical Sample
If no specimen was obtained, the State’s case relies entirely on the officer’s observations and Peterson’s performance on field sobriety tests. This is a significantly weaker case than one supported by chemical evidence.
Texas law defines intoxication in three ways under Penal Code Section 49.01(2):
- Not having the normal use of mental faculties by reason of the introduction of alcohol, a controlled substance, a drug, or a combination of two or more of those substances
- Not having the normal use of physical faculties by reason of the introduction of alcohol, a controlled substance, a drug, or a combination of two or more of those substances
- Having an alcohol concentration of 0.08 or more
Without a blood or breath specimen, the State cannot prove intoxication under the third definition (the per se standard). They must instead rely on the first two definitions, which require proof that Peterson did not have normal use of his mental or physical faculties.
To establish this, prosecutors will depend on:
- The officer’s observations (odor of alcohol, bloodshot eyes, slurred speech)
- Dash camera or body camera footage
- Peterson’s performance on Standardized Field Sobriety Tests (SFSTs)
- Any statements Peterson made
This type of case is often more defensible than a per se case because it relies heavily on subjective observations and tests that have significant room for error. As discussed above, when field sobriety tests are improperly administered, the State’s entire case can collapse.
The defense can argue that the officer’s observations are explainable by factors other than intoxication, that video evidence contradicts the officer’s testimony, and that field sobriety test results are unreliable due to improper administration. Without the “objective” evidence of a chemical test, these arguments become much more persuasive to a jury.
Retrograde Extrapolation – Challenging Chemical Test Results
If law enforcement did obtain a chemical specimen from Peterson, the analysis doesn’t end with the test result. A critical question remains: What was Peterson’s blood alcohol concentration at the time of driving, not at the time of testing?
Understanding Retrograde Extrapolation
Retrograde extrapolation is a forensic technique used to estimate a person’s blood alcohol concentration at the time of driving based on a BAC measurement taken later, typically at a police station or hospital. This becomes necessary because there is always a delay between when someone is stopped and when their blood or breath is tested.
The legal question is not “Was Peterson’s BAC 0.08 or higher when tested?” but rather “Was Peterson’s BAC 0.08 or higher when he was driving?”
Retrograde Extrapolation Calculator
The Critical Importance of Time of Last Drink
Another critical piece of information is the time of Peterson’s last drink. This seemingly simple fact has enormous implications for the scientific analysis of the case.
After consuming alcohol, the body goes through two phases: the absorption phase and the elimination phase. During absorption, alcohol is entering the bloodstream, and BAC is rising. During elimination, the body is metabolizing alcohol, and BAC is falling. The critical question is: Was the defendant in the absorption phase or elimination phase at the time of driving?
Consider this scenario: If Peterson’s blood was drawn an hour after he was stopped, and he had consumed alcohol within 30 minutes of driving, his BAC at the time of the test could actually be higher than it was when he was driving. This is because alcohol was still being absorbed into his system during and after the time he was driving.
Without knowing when Peterson last drank, any retrograde extrapolation becomes scientifically unreliable.
Challenging Retrograde Extrapolation
The defense can challenge retrograde extrapolation on several grounds when the time of last drink is unknown:
- The expert cannot determine whether the defendant was in the absorption or elimination phase
- Individual elimination rates vary significantly (typically 0.015 to 0.020 per hour, but can be higher or lower)
- Factors like food consumption, body weight, metabolism, and drinking patterns affect absorption and elimination
- Without reliable data points, any BAC calculation for the time of driving becomes speculative
This scientific uncertainty can create reasonable doubt, even when a test shows a BAC over the legal limit of 0.08. If the State cannot prove what Peterson’s BAC was at the time of driving—as opposed to the time of testing—they cannot meet their burden of proof under the per se definition of intoxication.
Furthermore, if Peterson was in the absorption phase when driving, his BAC at the time of driving may have been below 0.08 even if it tested above 0.08 an hour later. This creates a complete defense to the per se charge and forces the State to rely on the weaker “loss of normal use” definitions of intoxication.
Additional Challenges to Chemical Testing
Beyond retrograde extrapolation, chemical test results can be challenged on other scientific and procedural grounds:
- Equipment calibration and maintenance records
- Operator training and certification
- Testing procedure compliance
- Chain of custody documentation
- Observation period requirements (for breath tests)
- Partition ratio assumptions (for breath tests)
- Contamination issues (for blood tests)
- Coagulation and fermentation (for blood tests)
Each of these issues presents an opportunity to exclude chemical test evidence or to diminish its persuasive value to a jury.
Conclusion: The Importance of Thorough DWI Defense
Adrian Peterson’s case illustrates the complexity of DWI defense and the many potential weaknesses in the State’s case. From the initial stop to the final breath or blood test, numerous opportunities exist for procedural errors, constitutional violations, and scientific challenges.
Key questions remain unanswered: Was there reasonable suspicion for the stop? Did officers properly develop probable cause? If chemical testing occurred, can the results reliably indicate BAC at the time of driving? Were field sobriety tests properly administered? Each of these questions represents a potential defense strategy.
What appears in media reports as a straightforward case of intoxicated driving may actually involve significant factual and legal disputes. The difference between a conviction and an acquittal often lies in the thoroughness of the investigation into how evidence was gathered and whether proper procedures were followed.
For anyone facing DWI charges, whether a public figure or private citizen, the lesson is clear: these cases require detailed analysis by experienced defense counsel who understand both the scientific principles underlying DWI prosecution and the constitutional protections that limit law enforcement authority.
Protecting Your Rights After a DWI Arrest
If you’ve been arrested for DWI in Texas, the quality of your legal representation can determine the outcome of your case. The attorneys at Varghese Summersett have extensive experience challenging DWI evidence, from investigating the legality of the initial stop through cross-examining officers about field sobriety test administration.
We understand that every case is different and requires a tailored defense strategy based on the specific facts and evidence. Whether challenging retrograde extrapolation, filing motions to suppress evidence, or preparing for trial, our team has the knowledge and experience to provide aggressive, effective representation.
Don’t let procedural errors by law enforcement result in a wrongful conviction. Contact Varghese Summersett today for a consultation about your DWI case.
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