WILLIAMS, Calif. - A bus driver with a string of motor vehicle offenses and a history of substance abuse was arrested on suspicion of driving under the influence Monday, hours after his casino-bound charter bus ran into a ditch, killing eight people.

Investigators also said the bus had an invalid license plate, and they were looking into whether the driver had proper permits to operate the vehicle. The bus ran off the road Sunday while taking passengers to a northern California casino. About 30 people were injured.

Records show 52-year-old Quintin Watts of Stockton had been cited for speeding and other violations that resulted in loss of his license for nearly two years. He regained his driving privileges last January.

Watts was arrested as he lay critically injured in his hospital bed. His mother said he had wrestled with drug and alcohol problems, was jailed several times on drug charges and had smashed a car carrying a friend into a tree a few years ago, though neither was seriously hurt.

He was a longtime truck driver, but had been unable to find a trucking job since being released from jail on a domestic violence charge six months ago, his mother said.

Chaney Mae Watts said she believed the crash came on her son's first day behind the wheel of the bus after several training trips watching the owner drive. She and her husband told their son they were uncomfortable with him driving a vehicle that carried people instead of cargo.

"He wasn't the best driver," she said. "He knew we didn't want him to drive."

The accident was at least the eighth serious crash in the U.S. in the last three years involving buses carrying people to and from casinos.

Authorities were investigating whether prescription or nonprescription drugs or alcohol, or a combination, were involved in the crash. Blood test results are not expected for two to six weeks.

"We believe he was driving under the influence of something. That's why we placed him under arrest," said California Highway Patrol spokesman Robert Kays.

Another CHP spokesman, Patrick Landreth, said any criminal proceedings would be on hold while the driver is treated for his major injuries.

Colusia County District Attorney John Poyner said Monday it will be at least two to three months before the full accident reports are available and any criminal charges are made.

The bus carrying the driver and 42 passengers, many Laotian, was heading to the Colusa Casino Resort. According to a witness, it drifted off a rural two-lane road before the driver "overcorrected" and swerved back. The bus ejected some passengers as it rolled and crushed others, Landreth 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."

Families flooded hospitals looking for relatives who may have been involved in the crash.

Yvonne Haynes, 35, of Merced got a phone call Sunday night from her brother Tou Xiong, 29, saying there had been a bus accident. They started calling hospitals looking for their mother.

"We couldn't find her," said Xiong. "She came in as a Jane Doe. Her purse was lost in the accident and she did not have any ID."

Finally, at 3 a.m., the siblings found their mother at UC Davis Medical Center in Sacramento. Mai Cha, 74, of Sacramento has a broken rib, face and right wrist and with the tubes in her mouth, she cannot speak, said Haynes.

"She squeezed my hand so I know she hears me," said Haynes.

Their aunt also was an injured passenger, 67-year-old Ge Vue of Sacramento. Her son, Xou Xiong, 26, said his mother described the crash to him.

"All of a suddent the bus swerved and then it felt like the driver tried to come back to the road and that made it worse," Xiong said. "She said as soon as she felt the impact, she flew to the back. That's all she remembered. She got up and tried to look for my aunt and saw her laying there with another lady on top of her.

"She was shaking her, pulling her hand. She was trying to talk to her and she wasn't responding," Xiong said.

Laura Hennum, a spokeswoman for Enloe Medical Center, 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.

Ten victims were at the hospital Monday. Three in critical condition, four in fair condition and three in good condition.

The CHP identified the dead as Daniel E. Cobb, 68, of Sacramento and Modesto, and Lou Her, 68; Muang Saephanh, 68; Khou Yang, 67; Meuay Saelee, 74; Fin Saechae, 64; and Ma Vang, 60, all of Sacramento. Family members also identified Xee Vang, 87, of Sacramento.

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

"We sold it more than two years ago," said Kim Plaskett, the Greyhound spokeswoman. "It is an old bus."

Authorities said they were investigating if Cobbs Bus Services owned the bus, but refused to say why they focused on that company. They also wouldn't say if Cobb, who died in the crash, was the owner of the company.

The bus' last operator, listed by the DMV as the House of Prayer Apostolic Faith Christian Center of Modesto, has the same address as Cobbs Bus Service, a business registered to Daniel Cobb, according to the Public Utilities Commission.

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. "We will find out who owns the bus."

A man outside a home that is the primary listing for Cobb's business in Sacramento said the family was not ready to make a statement and declined further comment.

Don Kennedy, a spokesman for Colusa Casino, said Cobbs Bus Service has been busing players to the casino since 2006, between two and eight busloads a month.

Kennedy said Cobbs usually made advanced reservations, but was not scheduled to bring guests on Sunday. But he added the casino accepts unscheduled visits from charter buses.

"Our prayers and sympathy go out to all of the passengers, their families and anyone else who may have been affected by this accident," a statement from the casino said.

The statement said the casino does not own any charter buses, but they do everything they can to make sure that any company that organizes tours to bring guests to the casino is properly licensed, insured and regulated.

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Associated Press writers Juliana Barbassa, Malia Wollan and Marcus Wohlsen in San Francisco and Samantha Young and Juliet Williams in Sacramento contributed to this report. AP researchers Monika Mathur and Jennifer Farrar also contributed.