WILLIAMS, Calif. - The driver of a casino-bound charter bus that crashed and killed eight people is in critical condition and faces charges of driving under the influence, the California Highway Patrol said Monday.

Quintin Watts, 52, of Stockton was arrested on suspicion of driving under the influence. Authorities were investigating whether prescription or nonprescription drugs, or alcohol, were involved in Sunday's crash. They said it could be a combination.

Results of a blood test were not immediately released.

"We believe he was driving under the influence of something that's why we placed him under arrest," patrol spokesman Robert Kays said Monday.

The bus, which had an invalid license plate, drifted off a rural two-lane road before the driver "overcorrected" and swerved back, patrol spokesman Patrick Landreth said. The bus tumbled into a ditch, ejecting some passengers as it rolled and crushing others, police said.

"The roof was collapsed down, the windows were broken out, and the bus was not only rolled over onto its side, it rolled completely over," Landreth said. "It was facing the opposite direction and it was on its wheels."

The accident was at least the eighth in the last three years involving buses carrying people to and from casinos that caused deaths or multiple.

Watts had a valid commercial driver's license but the patrol is looking into whether he had the proper permits to drive a bus carrying passengers in California.

Officers are trying to determine the bus owner, but said based on a preliminary investigation, they're looking into a company called Cobbs Bus Service.

One of the dead was identified as Daniel E. Cobb, 68, of Sacramento and Modesto. Authorities did not confirm if he was the owner of Cobbs Bus Service. The CHP also identified five women killed in the crash including, Lou Her, 68; Muang Saephanh, 68; Khou Yang, 67; Meuay Saelee, 74; and Fin Saechae, 64, all of Sacramento.

The bus had "Greyhound" marked on its side. But a Greyhound official said it was no longer operated by the company.

"It is not our bus. We sold it more than two years ago," said Kim Plaskett, the Greyhound spokeswoman. "It is an old bus."

Kays said the bus had a Texas license plate that was "not valid." He said other registration serial numbers also came up invalid.

"There are still several pieces of this puzzle that's missing," Kays said.

The bus, which left from Sacramento, crashed 10 miles short of its destination, the Colusa Casino Resort. Many of the passengers were Laotian. The bus did not have seat belts, authorities said.

"It looks like they were going up to the casino to have a good time," CHP Commander Fran Clader said Monday. "Unfortunately, it resulted in tragedy."

Don Kennedy, marketing director at Colusa Casino Resort, said the bus was not scheduled to bring guests to the facility, but he added that the casino accepts unscheduled visits from charter buses.

Firefighters used flashlights and infrared sensors to search the tall grass near the overturned bus Sunday night for more victims. The mud-covered bus was pulled from the ditch and was on a large tow truck.

The crash took place in an area of rice fields and orchards a few miles east of Interstate 5 just north of Williams.

Laura Hennum, a spokeswoman for Enloe Medical Center, said 11 victims were at the hospital Monday morning. Four were in critical condition, one was in serious condition and six in fair condition.

She said one of the biggest challenges for the hospital was helping family members find one another, as passengers were taken to several hospitals.

"We were getting a huge volume of calls from distressed family members trying to find their loved ones," she said.

Some crashes involving casino buses in the past decade:

- Oct. 5, 2008: A casino-bound charter bus from Sacramento, Calif., crashes near Williams, Calif., killing eight people.

- Aug. 11, 2008: A shuttle bus swerves off a freeway near Las Vegas and slams into the center divider, injuring 29 casino and mall employees.

- Aug. 10, 2008: A casino bus full of tourists flips over in a median in Tunica, Miss., killing three people and injuring several others.

- May 17, 2008: A charter bus heading to the gambling town of Laughlin, Nev., overturns on a Mojave Desert freeway near Ludlow, Calif., killing a woman and injuring 22 other people.

- Jan. 17, 2008: A bus carrying workers to a casino on the Nevada-California line crashes into a guardrail and catches fire, injuring 25 people.

- Sept. 23, 2006: A bus returning from a casino rolls onto its side in a construction zone in Wright Township, Mich., injuring 11 passengers.

- Feb. 6, 2006: A bus from New York City to an Atlantic City, N.J., casino crashes through a guardrail and plunges 25 feet, injuring many of 53 passengers.

- March 15, 2005: A bus heading to a casino in Indio, Calif., smashes into a fire truck on a highway, killing one person and injuring 57.

- Oct. 9, 2004: A charter bus crashes in Marion, Ark., killing 14 people who had been headed to a Mississippi casino.

- May 24, 2004: A chartered bus carrying people back to Houston from a casino at Lake Charles, La., slams into a tractor-trailer near Anahuac, Texas, killing a woman and injuring many other people.

- Feb. 7, 2003: Tour bus taking passengers from New York City to Atlantic City, N.J., falls on its side on a slushy highway, killing two passengers and injuring 28.

- June 4, 2001: A bus carrying senior citizens to an Atlantic City, casino rams into a car on a New Jersey highway, killing the two people in the car and injuring dozens of bus passengers.

- April 9, 2001: A bus traveling from Mexico to a casino in Southern California swerves to avoid an accident, then overturns on a highway east of San Diego, injuring all 35 passengers.

- May 9, 1999: A bus heading to a casino in Bay St. Louis, Miss., runs off a highway on Mother's Day, killing 22 people. Investigators said the driver was impaired by severe medical conditions and use of marijuana and an antihistamine.

- Dec. 24, 1998: A bus headed for Atlantic City casinos skids off a highway and flips over in a ravine on Christmas Eve, killing eight people and injuring 15 others.