Toxicology tests show that the driver of a charter bus that crashed on a rural Northern California road, killing nine, was not drunk or on drugs at the time, prosecutors said Tuesday.

Many of the 42 passengers heading to Colusa Casino Resort when the Oct. 5 crash happened were Laotian seniors, and some remain hospitalized.

The driver, 52-year-old Quintin Watts, was released from the hospital and taken into law enforcement custody after he was released Tuesday morning from the hospital where he had been recovering from the crash.

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He was being held on suspicion of driving without a proper license at a Tracy prison while authorities continued their investigation. The California Highway Patrol initially arrested Watts on suspicion of driving under the influence after the bus overturned on a two-lane road.

Colusa County District Attorney John Poyner said Tuesday that the toxicology tests came back negative.

"At this point I don't know if the bus was defective. I just know he didn't have any drugs or alcohol in his system," Poyner said. "It could be anything from an accident that is very unfortunate or, if he committed gross negligence that could lead to manslaughter charges. I don't know if he fell asleep."

Watts, a longtime truck driver, told his family that he had been training to drive a bus, and the day of the crash was his first one behind the wheel, his mother, Chaney Mae Watts, has said. The owner of the bus was among those killed.

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