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The driver of a tour bus that crashed in Utah and killed three Japanese tourists last year formally apologized to families of the dead Tuesday, saying he deeply regrets his actions.

"I have made a great error, deeply hurt others, and have brought sadness into your lives, by the lack of my thoughts and by the big mistakes I have made," Yasushi Mikuni wrote in the three-page letter written in Japanese. An English translation of the letter was provided to The Associated Press by his Las Vegas attorney Garrett Ogata.

"Even though almost a year has passed since that accident, the visions of the guests' happy smiles on the way to Zion (National Park), then the scene just after the accident and at the hospital, are still flashing across my mind every day," Mikuni wrote.

The bus carrying 14 Japanese tourists was headed from Nevada to national parks in Utah on Aug. 9, 2010, when it rolled on Interstate 15, about 250 miles south of Salt Lake City. Three died and 11 others were injured.

Utah Highway Patrol investigators said that on the day of the crash, Mikuni, a 26-year-old Japanese citizen living in Las Vegas on a U.S. work and education visa, was driving on little sleep after a long work day the day before. Tests showed he also had marijuana in his system. Investigators said they didn't believe Mikuni was impaired while driving, but that he was sleep-deprived.

Killed in the crash were Hiroki Hayase, 20, of Osaka, Japan; and Junji Hoshino, 38, and his wife, Junko Hoshino, 40, from Shinjuku, Japan.

Mikuni was originally charged with 10 state felonies, but in May pleaded guilty to just three felony counts. He faces up to 15 years in prison when sentenced Aug. 5.

Ogata said the letter to the families is similar to what Mikuni intends to tell the judge in Cedar City next month.

"I have been spending every day regretting very many things," Mikuni wrote. "The various means I could have taken to avoid the accident, my judgment, my naivety. ... I yearn for the answers and it always concludes with these same last thoughts ... Why did I live, why have I survived this way?"

Mikuni, who suffered just minor injuries, was driving for Sandy, Utah-based Canyon Transportation Inc. He picked up the group in Las Vegas for a four-day tour of Utah's national parks and the Grand Canyon, according to troopers and tour organizers.

The bus had stopped at Zion National Park and was en route to Bryce Canyon National Park when it crashed. Utah Highway Patrol troopers said he flew to Salt Lake City and drove the tour bus to Las Vegas — about a seven-hour drive at the speed limit — the day before the crash, then got less than seven hours of sleep.

In the letter, Mikuni writes that he wonders if the crash could have been avoided if he consumed more energy drinks, slept more, or avoided smoking marijuana. The letter says working as a tour operator was Mikuni's dream job and expresses surprise that his family and others continue to support him despite the shame that his actions have brought.

Mikuni expresses his regret repeatedly throughout the letter and says his heart is heavy. He writes that he wants to talk about the accident in hopes of preventing future crashes.

He also asks the families to grant him their permission to continue with his own life.

"No time will be able to heal the loss of loved family members and I also understand that whatever I am trying to do, nothing will be able to compensate the loss," he wrote.

In addition to the criminal penalties Mikuni faces, the Hayase family has filed a personal injury lawsuit against him and the travel companies tied to the trip. Attorneys for the family say the Hayases and their daughter were also injured in the crash and that Akemi Hayase's injuries left her a paraplegic.

The lawsuit seeks unspecified financial damages for pain and suffering, medical expenses and funeral costs.

A similar federal lawsuit filed last October by Kei and Mai Maeda, who were on an anniversary trip at the time of the crash, has been dismissed. The Maeda's attorney, Scott Brown, said the lawsuit was refiled in state court about six weeks ago. A motion to merge the two lawsuits is pending, he said.

Court papers say Kei Maeda suffered a broken neck in the crash, and his wife suffered a punctured lung and an eye injury.