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Western Michigan University

How drunk? Estimates questioned in drunken-driving cases

The way prosecutors see it, Oneil Sharpe Jr. was drunk when he raced down a Long Island highway at nearly 100 mph this summer and slammed into a car carrying a family home from a church gathering, causing a fiery wreck that killed a father and his two children.

Sharpe's blood-alcohol reading, taken about four hours later, was 0.06 percent — below the legal threshold of 0.08. But he was still charged with drunken driving and vehicular homicide because a forensic technique estimated that his blood-alcohol level at the time of the crash actually was 0.12.

That technique, known as "retrograde extrapolation," has been used to win convictions nationwide for...