Updated

The lone bus belonging to a mom-and-pop tour operator careened off an interstate and overturned early Saturday, killing 15 Chicago-area travelers on their way to a Mississippi casino.

Witnesses told police the bus, which carried family and friends of the tour company owner, was drifting.

The bus was about 30 miles short of its destination in Tunica, Miss., (search) when the crash happened about 5 a.m. on Interstate 55 in northeastern Arkansas, near Memphis, Tenn.

Thirty-one people were aboard, and the remaining 16 passengers all were injured, many critically. Some of the dead were found crushed beneath the bus after wrecker crews pulled it upright, state police spokesman Bill Sadler said.

Among the dead were the bus owner's brother, who had been driving, and the owner's wife. The driver, Herbert Walters, was believed to be in his 60s.

Witnesses told police the bus drifted off the road near a point where the interstate veers to take travelers into Memphis.

The bus, "just kind of faded over there," said Cpl. Mickey Strayhorn of the Arkansas State Police. "There was not really any erratic driving before this occurred."

A light mist was falling at the time of the crash, but visibility did not appear to be significantly limited, police said.

The impact tore off a section of the bus' roof, and emergency workers had to shear off the rest of the top to reach a trapped passenger.

Tracks in the grass showed the bus went straight rather than around the curve, then hit a ditch and flipped over. There were no skid marks.

"They had to cut it [the roof] free from the bus, but it was peeled off more or less," Strayhorn said.

Other victims, thrown from the bus, were scattered among grass and weeds at an interstate exchange, along with popped-open suitcases and other belongings.

Sgt. David Moore, describing the force of the impact, said it would be "similar to an explosion. There were people everywhere."

Assistant Fire Chief John Burns of West Memphis said when he and a crew of firefighters arrived at the scene, "there was nobody walking around — everybody was laying down.

"It wasn't the scene where you see everybody screaming and crying for help," Burns said.

State police had a partial list of passengers and were going through debris to identify the others.

Sadler said 15 people were dead, but he said later the number of victims was 14, though he could not account for the last of the 31 people on the bus. Fire officials said 13 people died at the scene and two others died at hospitals.

Sandy Snell, spokeswoman for The Medical Center at Memphis, said that hospital was treating eight victims, including three in very critical condition, three in critical condition, and two with serious injuries.

Witnesses and survivors told police the trip was uneventful, then "the next thing we knew, we were off the road," Sadler said.

The bus went down a slight incline and flipped as it cut through a ditch, stopping about 100 yards from the highway.

Roosevelt Walters, who operated Walters Charter and Tours (search) of Chicago, said his wife was aboard the bus because she had organized the trip for a group of friends, retirees and teachers. He said his brother, Herbert Walters, was driving.

Without hours of learning about the crash, Walters also learned that his wife and brother had been killed.

"This thing that happened, nobody has an answer for. All we can do is direct them to God," said the Rev. Curtis Reed, who was serving as a family spokesman.

Police cautioned that investigators may not know what happened for weeks.

"There'll be so many things they'll need to look at," Sadler said.

Both Roosevelt and Herbert Walters held commercial driver's licenses issued to drivers of large trucks and tour buses, said Dave Druker, a spokesman for the Illinois secretary of state's office.

Records dating back about 10 years indicated both had clean driving records, with no tickets or violations, Druker said.

The Federal Motor Carrier Safety Administration (search) also had no record of accidents or inspections of Walters' bus company during the last two years, said spokesman David Longo.

The company's last comprehensive safety review by the federal agency was in 1987, when it received a "satisfactory" rating.

Walters said he inspected the vehicle, his only tour bus, on Friday and found it to be in good mechanical shape.

The group left from his home Friday evening and had planned to spend the weekend at a casino, then return to Chicago by Monday night.

The bus made the trip twice a year, and most of those in the group knew each other. Walters said his stepson, his sister-in-law, a cousin and his neighbors were also aboard.

Fredonia Gay, who lives three miles from the crash site, was awakened by passing medical helicopters.

"The helicopters kept coming over my house, and I knew it would be something tragic," she said. "They kept coming and coming."

The National Transportation Safety Board (search) planned to join the investigation.

The accident occurred about 13 miles from Marion, Ark., just outside Memphis, Tenn.