A few weeks ago a Tennessee police officer, Ronald Killings, was acquitted of reckless homicide charges by a jury of his peers. The defense presented the events as a case of an officer discharging his duties confronted unexpectedly by a child who darted out in front of his car. And, had that been the whole story, I would have agreed that the prosecution was entirely wrong to have placed a police officer on trial for such an accident.

However, the judge prohibited the jury from hearing about charges that Mr. Killings destroyed evidence of open liquor bottles in his unmarked car and from hearing the nature of certain conversations in which he was engaged while speeding through a residential neighborhood.

The jury heard only that Mr. Killings was engaged in a personal cellphone conversation after he increased his speed to reach the scene of a police stakeout. In Tennessee, it’s legal to use a cellphone and drive. Apparently, there’s no requirement, either, for hands-free use, but Mr. Killings testified nonetheless that the cellphone was in his lap and fell on the floor of the car upon impact, even though an eyewitness saw him exit the car with a cellphone to his ear.

A February 16 article in Science News, by Bruce Bower (“Cell Phone Distraction while Driving Is a Two-way Street”) suggests that police drivers should think twice before they accelerate when conversing on their two-way radios, let alone their personal cellphones. According to the article, a researcher at the University of Illinois (psychologist Gary Dell) has shown that not only does cellphone use impair driving ability, but driving also impairs comprehension of cellphone conversations. Dr. Dell says, “although many drivers regard talking while cruising a straightaway as no harder than walking while chewing gum, ‘that intuition is incorrect.’”

During the study, Dr. Dell told stories to drivers on cellphones, including one about a robbery. When asked to repeat the story, drivers were able to relate as few as half of the facts correctly.

Given this study, perhaps Murfreesboro, TN, law enforcement will rethink its policies on personal cellphones in police cars.

If so, I hope it will also consider that Mr. Killings not only was talking on a cellphone while speeding through a residential neighborhood, but he was simultaneously conversing with a fellow officer: testimony at the trial was that an officer called for Mr. Killings’ assistance at a robbery stakeout while he was on his personal cellphone. If Dr. Dell’s study is correct, Mr. Killings likely did not fully comprehend the nature of the scene to which he was being called.

Imagine how many people’s lives might have been put at risk if he had reached the stakeout only half aware of what was happening there.