NEW YORK — A bus driver accused of being so tired that he caused a crash that killed 15 passengers was found not guilty on all felony charges by a jury on Friday, underscoring the difficulty in prosecuting so-called drowsy driving cases.
The driver, Ophadell Williams, was returning to New York from an overnight trip to the Mohegan Sun Casino in Connecticut in March 2011 when his bus struck a guardrail on Interstate 95, flipped over, and smashed into a signpost with enough force to shear off part of the roof.
The crash — one of the deadliest in the city’s history — also injured many other passengers, including one man whose arms were torn off as he tried to shield his face.
After nearly two weeks of deliberations, the jury in state Supreme Court in the Bronx acquitted Williams of 53 of the 54 charges, the most serious of which were criminally negligent homicide and manslaughter. He was found guilty on a single charge of aggravated unlicensed operation of a motor vehicle, a misdemeanor.
Williams, 41, showed visible relief as the verdict was announced in the courtroom, at times wiping his eyes and putting his face in his hands. He has been in prison since September 2011 after he was unable to post a $250,000 bail.
The verdict was a blow to prosecutors in a precedent-setting case that had stretched on for nearly two months.
Lacking any direct measurement of fatigue, they called 55 witnesses in an exhaustive attempt to answer the central question of whether Williams was, in the words of one prosecutor, suffering from ‘‘sleep deprivation so severe that it affected his reflexes the same as if he was intoxicated.’’
Traffic safety advocates hoped that it would send a strong warning about the risks of drowsy driving.