SALT LAKE CITY—Investigators say the driver of a tour bus that careened off a Utah highway had been smoking marijuana heavily for days before the deadly accident but wasn't legally impaired while driving.

Instead, fatigue caused Yasushi Mikuni to drift off Interstate 15 near Cedar City and flip the shuttle bus Aug. 9, leaving three members of a Japanese tour group dead and 11 other passengers injured, Utah Highway Patrol Sgt. Ryan Bauer said Wednesday. He was released on a $50,000 bond early Thursday, and his first court appearance scheduled for Oct. 19 in Cedar City.

Tests showed Yasushi Mikuni had traces of the active ingredient of pot in his system, and he "admitted to smoking marijuana heavily over the past several days," according to an arrest record. "He admitted to being sleepy at the time of the crash and unfocused."

Mikuni, 26, was charged Wednesday with 10 felony counts of negligent driving under the influence and one misdemeanor charge of having marijuana residue in his system. He also faces misdemeanor logbook violation and unsafe lane-change charges.

Mikuni is a Japanese citizen who lived in Las Vegas on a work and education visa.

He flew to Salt Lake City and drove the bus to Las Vegas before setting out the next day for a tour of national parks -- with seven hours sleep, nicotine gum and energy drinks, the Utah Highway Patrol said.

"The main reason we feel this accident happened was that he was driving too many hours and didn't have enough sleep the night before," Bauer told reporters in a teleconference call Wednesday from Cedar City.

Investigators don't believe Mikuni was impaired while driving, Bauer said. But Utah law doesn't allow a driver to have even a trace of an illicit drug in his or her system, and "that's something he's going to have to answer for," he said.

Mikuni was arrested Monday in Cedar City after volunteering to travel from Las Vegas for an interview with investigators. That saved Utah prosecutors from having to issue an arrest warrant and extradite him from Nevada, Bauer said.

Mikuni was accompanied by his father and a brother. They also visited the accident scene with troopers.

"It's pretty obvious he's feeling terrible about this," Bauer said.

Mikuni could face up to 50 years in prison if convicted on all of the felony negligence charges, which stem from the deaths of three passengers and the serious injuries that seven others suffered.

Bauer said Mikuna had a lawyer, but the sergeant Thursday didn't know the attorney's name. Jail officials said Thursday they had no record of the lawyer. None was listed on a court docket, and 5th District clerks said they didn't know.

Mikuni, who escaped the accident with minor injuries, was driving for Canyon Transportation Inc. of the Salt Lake suburb of Sandy. He picked up 14 Japanese tourists in Las Vegas for a four-day tour of Utah's national parks and Arizona's Grand Canyon, according to troopers and tour organizers.

The bus had made a stop at Zion National Park and was en route to Bryce Canyon National Park when it rolled over.

Hiroki Hayase, a 20-year-old man from Osaka, Japan, was killed in the crash, along with Junji Hoshino, 38, and his wife Junko Hoshino, 40, from Shinjuku, Japan.

Canyon Transportation declined comment, referring the AP to a Salt Lake City lawyer who wasn't available. Bauer said no charges have been filed against the company, but it faces a federal inquiry for operating across state lines without a license.

Bob Kelleher, the Utah administrator for the Federal Motor Carrier Safety Administration, has said the bus company wasn't supposed to do business outside of Utah. It typically picked up passengers from Salt Lake City's airport for short rides to ski areas, he said.

The status of that investigation wasn't immediately clear Thursday.

Canyon Transportation supplied the 2006 Ford E350 shuttle bus and driver to other tour operators who organized the trip. One of those organizers, Keith Griffall, CEO and co-owner of tour organizer Western Leisure Inc., has told the AP he was unaware that Canyon Transportation lacked the proper federal license.

Griffall said his company and Nippon Travel Agency in Tokyo were among several companies that helped organize or provided customers for the tour.

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