The crash on Interstate 40 in North Little Rock happened yesterday at about 1 am, in light rain and fog following a heavy storm, but it wasn't immediately known whether weather played a role.
The National Transportation Safety Board investigation is initially focusing on the possibility of driver fatigue, though investigators may focus on other issues once they're on the scene, spokesman Eric Weiss said.
Of those who died, three were thrown from the bus, one was partially ejected and the other two died inside, said Col Bill Bryant, the head of the Arkansas State Police.
Vasquez has agreed to routine drug and alcohol tests, but there's no indication he was intoxicated, state police Maj Mike Foster said.
A woman who answered the phone yesterday at the Lake Placid, Florida-based company hung up as The Associated Press sought more information.
Twelve survivors of the crash are from Mexico, according to a list released late yesterday afternoon by Arkansas State Police. Three others live in Florida, while police didn't have a residence for another survivor. Their ages range from 19 to 43. The names of those killed are being withheld until all families have been notified, police said.