Story highlights Ophadell Williams, 41, is guilty of aggravated unlicensed operation of a motor vehicle

He was acquitted of manslaughter and criminally negligent homicide

The March 2011 crash killed 15 passengers and injured 18 others

The bus driver charged in a March 2011 crash that killed 15 passengers and injured 18 others in New York was acquitted of manslaughter and criminally negligent homicide charges Friday.

Ophadell Williams, 41, was found guilty of aggravated unlicensed operation of a motor vehicle in the third degree. He has served more than 15 months in prison and was sentenced to an additional 30 days. He will also pay a $500 fine.

A jury in the Bronx reached the verdict Thursday afternoon, but the judge delayed the reading to Friday morning because a juror had to leave for a medical appointment.

The crash occurred just before 5:40 a.m. on Interstate 95 near the Bronx-Westchester County line. The bus was carrying 32 passengers from Mohegan Sun Casino in Uncasville, Connecticut, and was headed for Chinatown in Manhattan. Investigators determined that after crossing a 10-foot shoulder, the bus struck a guardrail, skidded 500 feet and slammed into two signposts that tore off nearly the entire roof of the bus.

An investigation ordered by New York Gov. Andrew Cuomo found that Williams was able to obtain a commercial bus license by allegedly using false information.

Williams had claimed that a tractor-trailer clipped the bus, causing the accident, but a March 2011 National Transportation Safety Board investigation found no evidence supporting the claim.

Investigators also determined that Williams was driving 78 mph in a 50-mph zone at the time of the accident.

In June 2012, NTSB investigators concluded that Williams was sleep-deprived while driving and that the combination of fatigue, poor sleep quality, excessive speed and poor oversight resulted in the fatal collision.

World Wide Travel, the bus company, was shut down after the accident. The NTSB subsequently launched a broad investigation into the country's tour bus industry and its safety regulations.