When Science Doesn’t Prove Impairment: Understanding DUI Evidence in New Hampshire

In New Hampshire, a DUI conviction requires proof beyond a reasonable doubt that the driver was under the influence “to any degree which impairs the person’s ability to drive safely.” Yet blood test results and the presence of substances like alcohol or THC do not automatically establish impairment. A recent case handled by Apis Law demonstrates how laboratory data—without retrograde analysis, field testing, or corroborating evidence—can fail to meet this burden.

Apis Law - Represents Defendants Charged with DUI

Background: How DUI Evidence Works in New Hampshire

Under RSA 265-A:2, prosecutors must prove actual impairment, not just the presence of alcohol or drugs. A blood alcohol concentration (BAC) at or above .08 creates a presumption of impairment, but anything below that threshold requires independent evidence—such as erratic driving, failed field sobriety tests, or expert toxicology testimony—to connect the lab result to driving behavior.

For cannabis, the law is even less clear. There is no statutory “legal limit” for THC, and state labs explicitly avoid interpreting whether a detected level means impairment. Because THC is fat-soluble and lingers in the body, a “positive” finding can reflect prior use unrelated to the time of driving.

Case Example: Interpreting a .04 BAC and “Positive” THC Result

In this case study, a driver consented to a voluntary blood draw two hours following a single-car rollover accident in Nashua. The New Hampshire State Police Forensic Laboratory reported an ethanol level of 0.048 ± 0.003 g/100 mL, well below the per se limit of .08. The lab also detected Delta-9-THC and its metabolites at or near the limit of detection (1–2.5 ng/mL) . There was no quantitative analysis performed on the THC.

Critically, the report states:

“This report does not offer a statement or opinion of impairment specific to a given individual.” 

No retrograde extrapolation was performed to estimate the BAC at the time of the crash, and no Drug Recognition Expert (DRE) evaluation or standardized field sobriety test (SFST) was conducted. Without these analyses, the mere detection of alcohol or THC does not establish impairment at the time of driving.

Missing Foundations in the State’s Case

The physical evidence also left unanswered questions:

• No accident reconstruction report was ever completed to determine how or why the vehicle rolled.

• The officer never asked the driver how the accident occurred, despite darkness and heavy rain in a street-lit area—conditions that easily could have caused a loss of control unrelated to intoxication.

• The bottle of alcohol found in the car was never traced to the driver’s possession or control before the crash. Given that the car overturned, it is equally plausible that the bottle spilled, producing the strong odor that officers noted.

• At the hospital, no treating physician documented alcohol odor or intoxication symptoms.

Despite these gaps, the state relied on circumstantial evidence—the smell of alcohol, the open bottle, and statements about drinking—to justify a DUI charge.

Scientific Context: Why the Numbers Don’t Add Up

A BAC of .048 is not consistent with consuming “two to five shots” within an hour or two, as was alleged. Without knowing when the drinking occurred or performing retrograde analysis, the state cannot show that the driver’s BAC was higher at the time of operation. Moreover, THC results in this range (1–2.5 ng/mL) fall within the laboratory’s detection threshold—meaning the lab confirmed only presence, not concentration.

These limitations matter. Toxicology science distinguishes between detection (finding a substance) and quantitation (measuring an amount). Only the latter can support any inference of impairment, and even then, expert testimony is required.

Outcome: A Negligent Driving Plea

In the end, prosecutors agreed to amend the charge to negligent operation, recognizing the absence of evidence proving impairment. The Department of Safety independently declined to suspend the driver’s license, citing the .04 BAC result as below the legal limit. The case underscores the principle that scientific results must be interpreted in context, not assumed to be proof of guilt.

Takeaway for Drivers and Defense Attorneys

This case highlights several lessons regarding DUI Evidence in New Hampshire:

1. Lab reports alone do not prove impairment. The state’s own toxicology disclaimer makes that clear.

2. Retrograde analysis is essential if prosecutors want to connect a post-incident BAC to the time of driving.

3. Weather, lighting, and road conditions remain crucial factors in accident causation.

4. Cooperation matters. Voluntary consent to testing often signals a lack of consciousness of guilt.

5. Defense strategy must focus on science. Understanding analytical limits and forensic uncertainty dismantles weak DUI cases.

If you are facing a DUI or negligent operation charge in New Hampshire, the scientific and procedural details of your case can make all the difference. Contact Apis Law to discuss how lab reports, accident reconstruction, and evidentiary standards apply to your defense.