What Good are Defence Counsel Experts Anyways?

They are a bit like the grit in an oyster. The oyster doesn’t like it, but rather than complain and be irritated all the time, you can make a pearl out of it. I feel my “pearls” were the numerous papers I published, the large computerised alcohol database of about 11,000 studies, and my encyclopaedic book “Wigmore on Alcohol“, all produced in part by the prodding of defence experts and lawyers.

The challenges posed by defence counsel push forensic experts to refine their methodologies, strengthen their documentation, and communicate their findings with greater clarity. This adversarial pressure elevates the quality of forensic science itself, benefiting personal injury cases, overserving liability matters, and criminal proceedings alike.

A recent study also found another important role of defence experts in mitigating invalid prosecution expert testimony.

Researchers Eastwood and Caldwell, presented a mock sexual assault case based on the wrongful conviction of Clavin Lee Scotts to 155 participant “jurors”. All jurors were given the basic outline of the mock case. The victim was sexually assaulted in her home. She could only identify the assailant as being a black male of medium build. The accused’s alibi was that he was alone at home and it was noted that he provided hair samples.

Ninety-five per cent of the control group that were only given this information found the defendant “not guilty”. The other 4 groups of participant jurors were then also were given the testimony of the prosecution hair expert who examined the hairs found on the victim’s bed and the hairs from the accused and testified that they were “microscopically consistent”. The expert also stated that the probability of the hairs found with the victim belonging to anyone other than the accused was quite small.

One of the juror groups then received no additional forensic information (no education) and the “not guilty” rate dropped to only 50%. When the jurors were given additional forensic information by the judge alone, about the limitations of hair analysis, the “not guilty” rate increased but the increase was statistically not significant. It was only when the jurors were given the testimony of the defence expert or of the defence expert and judge’s instructions was the “not guilty” rate significantly increased and mitigated the effects of the invalid and overstated forensic evidence. (see following Graph)

This research demonstrates a critical function that defence counsel experts provide beyond simply challenging prosecution evidence. They serve as essential safeguards against invalid or overstated forensic testimony that might otherwise mislead juries. In personal injury and overserving liability cases, this protective role proves equally vital.

When prosecution experts overstate the certainty of blood alcohol calculations, extrapolate beyond scientifically supportable conclusions about impairment timing, or misrepresent the reliability of THC detection methods, defence counsel experts provide the counterbalance necessary for accurate fact-finding. Without this adversarial testing, flawed forensic evidence goes unchallenged, potentially leading to unjust outcomes.

At Wigmore on Alcohol, we’ve witnessed how defence counsel experts strengthen civil litigation involving alcohol-related incidents. In overserving liability cases, for example, prosecution experts may present simplified timelines of alcohol absorption and elimination that fail to account for individual variation, food consumption effects, or methodological limitations in blood alcohol testing.

Defence counsel who retain qualified forensic toxicology experts can expose these oversimplifications, ensuring that judges and juries receive complete, scientifically accurate information. This adversarial process doesn’t obstruct justice—it enhances it by demanding rigour and precision from all expert testimony.

The study’s findings apply directly to personal injury litigation where forensic evidence plays a central role. Whether evaluating impairment in motor vehicle accidents, assessing liability in premises cases involving intoxication, or determining causation in injury claims, the presence of competent defence counsel experts elevates the quality of evidence presented to the court.

The authors concluded that:

The judicial instruction were shown to have no impact on verdict decision. These findings suggest that providing opposing expert testimony may be an effective safeguard against invalid forensic testimony in criminal trials.

This conclusion validates what experienced forensic scientists eventually learn: defence counsel experts aren’t obstacles to justice but essential participants in achieving it. Over 700+ cases of testimony experience has reinforced this understanding. The questions posed by defence counsel, the alternative interpretations offered by defence experts, and the rigorous scrutiny applied to prosecution evidence all contribute to more accurate, reliable outcomes.

For personal injury and overserving liability cases requiring forensic toxicology expertise, Wigmore on Alcohol provides the scientifically sound, thoroughly documented expert testimony that withstands adversarial challenge—whether supporting plaintiffs or assisting defence counsel in protecting their clients’ interests.

References
Eastwood, J., and Caldwell, J., “Educating Jurors about Forensic Evidence: Using an Expert Witness and Judicial Instructions to Mitigate the Impact of Invalid Forensic Science Testimony”, Journal of Forensic Sciences, 60(6): 1523-1528, 2015