Science of estimating earlier drunkenness worth questioning

If you choose to drink, hopefully you don’t drink and drive. The risks that anyone in Tennessee faces from such behavior are something that is hammered home on a regular basis. If you drink and drive, you pose a threat to yourself and others on the road.

Social outrage at the injuries and loss of lives due to drunk driving has motivated lawmakers across the country to crack down hard on those convicted of such offenses. And as we have noted in this blog before, even the mere leveling of drunk driving charges can prove devastating when a person is charged. That makes mounting a strong defense critical.

Forensic science is one of those tools that authorities have come to rely on to present purportedly solid evidence to the court and to juries. It makes good sense. Most science is understood to be based on exact laws that can’t be refuted — except when it isn’t. And it is in those latter instances when purported science deserves to be challenged.

There is one irrefutable scientific fact about consuming alcohol. It is that it begins to be flushed from the system at some point after the drinking stops. This can present major incentives for law enforcement to get a blood alcohol tests as soon as possible after an arrest. If they wait too long, the reading may be below the .08 percent level for drunk driving.

One way prosecutors have used to get around this possible issue is a forensic technique called “retrograde extrapolation.” The way it works is that a forensic expert estimates what the blood alcohol content of a suspect might have been at the time of the alleged criminal act based on several assumptions and the BAC level of the person measured long after the fact.

The technique has been used for decades in many states, including Tennessee, to win DUI convictions. But many with experience in criminal defense say every body deals with alcohol differently and so retrograde extrapolation deserves to be challenged whenever it is used.

With all the tools prosecutors bring to bear and all that is at stake, anyone facing charges should be prepared to seek the counsel of a skilled attorney.

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