The bus, No. 1115, was en route from Louisville to Atlanta when it crashed at 6:15 a.m. EDT, Greyhound spokeswoman Karen Chapman said. The crash happened about 50 miles southeast of Nashville on Interstate 24.
Two senior federal law enforcement officials told The Associated Press that the FBI has found no immediate connection between the crash and the terrorist investigations. Law enforcement officials said it appeared to be random violence, but that they were investigating all possibilities.
"We don't have any indication throughout our system that this is part of any pattern," Chet Lunner, a spokesman for the U.S. DOT, told CNN.
An official from Middle Tennessee Medical Center in Murfreesboro, TN, said the driver was treated for a laceration of the neck and was stable after surgery.
Steve DeFord, a spokesman for the Coffee County Sheriff's Department, said the suspect was among those killed. He said FBI agents were among the investigators at the crash site.
Passenger Carly Rinearson called Nashville TV station WTVF by cell phone and said that a man who appeared to be 30 to 35 years old kept approaching her front seat and asking what time it was. She said the man then asked if he could have her seat, and she refused.
Afterward, Rinearson said, "he just went up to the bus driver and, like, slit his throat, and the driver turned the wheel and the bus tipped over."
Greyhound announced service will resume today at noon CDT.