The bus driver charged in a crash that killed 15 tourists on the way back from a casino knew the risks of fatigue but chose to drive sleep deprived anyway, prosecutors said Thursday at the first day of his manslaughter trial, reports the New York Daily News.

Ophadell Williams was driving the bus from a Connecticut casino to Chinatown on March 12, 2011 when he lost control on Interstate 95 as the vehicle entered the Bronx, killing 15 passengers. Prosecutors believe he fell asleep at the wheel and crashed the bus as a result.

His defense has said Williams got plenty of rest and was not asleep when the accident occured.

Williams has pleaded not guilty to manslaughter and criminally negligent homicide.