NEW YORK CITY, N.Y. -- The driver in the deadly tour bus crash on a New York City highway last year may have been overtired. Documents released by the National Transportation Safety Board show driver Ophadell Williams may not have had the sleep he claimed in the days prior to the accident.

The tour bus crashed last March while returning to Manhattan from an overnight trip to a Connecticut casino. 15 people were killed.

The documents show three days before the accident, Williams' cell phone and rental car were in constant use during the time he claimed to be sleeping. Williams had maintained he was alert and awake when the crash occurred.

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