(CNN) -- New York's governor, citing questions about the driver's "criminal record and driving history," on Monday ordered the state's inspector general to investigate how a Brooklyn man got licensed to drive a bus that crashed over the weekend, leading to the deaths of 15 people.
The driver, 40-year-old Ophadell Williams, has not been charged. Police said Williams told investigators that the incident occurred early Saturday after he swerved to avoid a tractor-trailer that might have clipped the bus. The bus then flipped on its side and smashed into the poles, which cut through two-thirds of the vehicle.
Gov. Andrew Cuomo directed Inspector General Ellen Biben to "commence an immediate investigation" in light of issues related to Williams' "criminal record and driving history." In a statement, Cuomo questioned why Williams was able to get and keep a commercial driver's license.
Staff from the inspector general's office will coordinate with the New York state police, as well as the Bronx district attorney's office, in the investigation, according to Cuomo.
Williams fatally stabbed a man about 20 years ago, leading to a manslaughter conviction, said New York Department of Correctional Services spokeswoman Linda Foglia. He served three of the nine years he was sentenced, from 1992 to 1994.
He was later convicted of grand larceny, leading him to spend parts of the years 1998 to 2002 behind bars, according to Foglia.
A New York City official said Monday that a 15th person had died because of injuries related to the crash, which took place in the Bronx, about 5:30 a.m. on a stretch of I-95 called the New England Thruway not far from Westchester County. The bus had left the Mohegan Sun Resort and Casino in Uncasville, Connecticut, and was bound for Chinatown in Manhattan, according to news reports.
Along with those killed, at least seven of the 31 passengers suffered severe injuries and were transported to area hospitals with the remaining survivors. At least five people being treated at New York's St. Barnabas Hospital suffered skull and spinal fractures, internal bleeding and broken bones, Dr. Ernest Patti told reporters.
Williams suffered "non-life threatening injuries," police said.
Police recovered a tractor-trailer that was traveling through the area at the time and interviewed its driver. The driver of the tractor-trailer denied that two vehicles collided before the bus crashed, a law enforcement source told CNN.
Federal investigators are considering other potential causes of the crash, including mechanical problems, steering and brake issues as well as the possibility the driver fell asleep. Some surviving passengers, according to news reports, told police that they felt the bus roll over rumble strips before the crash.
At a Sunday afternoon press conference, National Transportation Safety Board Vice-Chairman Christopher Hart said investigators are looking for video recordings taken at the casino and, possibly, an electronic hotel key card that might track some of Williams' activities within 72 hours of the accident.
Investigators previously admitted they are examining Williams' background and testing his blood for the presence of alcohol. Police officials also have said they are looking into the possibility that Williams had been speeding prior to the accident. Two UPS couriers told CNN affiliate WABC-TV that they twice saw the bus traveling very fast on the highway before the accident.
In addition, records on the Federal Motor Carrier Safety Administration website show that the bus line involved -- World Wide Travel -- was involved in a crash in New York in 2009 that resulted in one injury, and a crash in New Jersey in 2010 resulting in one injury.
The company has been cited five times for "fatigued driving" between December 2009 and October 2010 -- twice in in New Jersey, twice in Pennsylvania and once in Connecticut, records show.