Cross-Examining the Field Sobriety Opinion in a Massachusetts OUI Trial

The Commonwealth’s OUI case usually arrives as an opinion. The officer describes the stop, the eyes, the speech, the exercises on the shoulder of the road, and then the conclusion built on all of it. Juries take opinions seriously, and they should, until the opinion is examined. This post describes how that examination works in this office, and it accompanies our new page on field sobriety and breath test defense and our new field sobriety and breath test FAQs.

The Opinion Has Three Legs

A field sobriety opinion stands on the administration of the exercises, the observation of the performance, and the interpretation of what was seen. Each leg can be tested. The administration is measured against the NHTSA manual the officer trained on, which prescribes one way to give each test and warns that changes compromise validity. The observation is measured against the scene: darkness, strobes, traffic, wind, cold, the slope and surface of the shoulder, and the state of a nervous driver at midnight. The interpretation is measured against the manual’s own numbers, which report modest accuracy at predicting blood alcohol level and say nothing about impairment behind the wheel. An opinion with three unsteady legs does not hold much weight by the end of the examination.

The Manual Belongs to the Defense

The most useful documents in an OUI trial were written by the government. The NHTSA manual sets out the standardized elements, the required instructions, the scoring clues, and the populations and conditions the tests were not designed for, including drivers over 65, drivers with back, leg, or inner ear problems, drivers more than 50 pounds overweight, and any surface that is not dry, hard, and level. The officer trained on that manual and certified on it. The cross-examination asks the officer to agree with his own training, one sentence at a time, and the agreement usually comes, because the alternative is to argue with the book that certified him.

Confirmation Bias Has a Paper Trail

Most reports record clues and omit everything else. The driver who produced his license without fumbling, answered questions in complete sentences, stepped out without holding the door, and stood without swaying earns no line in the narrative, because the investigation reached its conclusion before it reached the exercises. Cross-examination rebuilds the missing column: what was done well, what was never tested, and what the officer would have expected from a truly impaired driver that this driver never showed. The jury watches the scale rebalance as the answers accumulate.

Calm Is the Method

None of this requires a raised voice, and none of it happens from a script. Attorney Serpa questions without notes, listens to every answer, and lets the officer’s answers supply the next question. The tone stays respectful, because the jury’s respect follows the questioner who is fair to the witness, and because a fair examination leaves the witness no one to fight. By the time the final questions arrive, each one has been built by the answers before it, and the witness agrees because the record he helped create leaves nothing else to say. The method is described more broadly on our page on cross-examination in Massachusetts criminal trials and in our post on the two rules of cross-examination.

What This Means for a Pending Case

A driver facing an OUI charge should not assume the roadside opinion decides anything. The exercises have documented limits, the observations have context, and the conclusion has alternatives that were never investigated. The related license questions are collected in our Massachusetts OUI FAQs and our license suspension guide, and a second offense with a decade-old prior may qualify for the Cahill second-chance disposition. Call 617.936.0201 for a free, confidential consultation.