Updated

The 26-year-old driver of a tour bus that crashed in Utah and killed three Japanese tourists last year pleaded guilty Tuesday to reduced charges.

As part of an agreement with prosecutors, Yasushi Mikuni made the plea to three counts of operating a vehicle negligently causing serious injury or death. In exchange, prosecutors dropped seven other felony and three misdemeanor charges, defense attorney Keith Barnes told The Associated Press.

Mikuni could face up to 15 years in prison at his sentencing, set for Aug. 5 in 5th District Court in Cedar City. Prosecutors have agreed to recommend that the sentences are served concurrently, Barnes said.

Utah Highway Patrol investigators said that on the day of the crash, Mikuni was driving on seven hours of sleep, nicotine gum and energy drinks. Investigators have said they didn't believe Mikuni was impaired while driving, but that he was sleep-deprived.

His lawyer told the AP that Mikuni "has been very remorseful and feels great sorrow for what he has done. He wants the victims in the case to have some closure. Mr. Mikuni would also like some closure for himself, so that's why, under these difficult circumstances, this was the right plea."

Barnes said Mikuni is drafting a letter expressing his remorse to the families of the victims and that the Iron County attorney's office has been asked to distribute it on his behalf.

A message left for county attorney Scott Garrett was not immediately returned.

Mikuni is a Japanese citizen who lived in Las Vegas on a work and education visa. He has been free on $50,000 bond and will remain free pending the sentencing, Barnes said.

The tour bus carrying 14 Japanese tourists was headed from Las Vegas to national parks in Utah when it rolled over on Interstate 15, about 250 miles south of Salt Lake City.

Mikuni, who escaped the accident with minor injuries, was driving for Canyon Transportation Inc. of the Salt Lake City suburb of Sandy. He picked up the group 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 stopped at Zion National Park and was en route to Bryce Canyon National Park when it rolled over. Utah Highway Patrol investigators 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.

"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," UHP Sgt. Ryan Bauer said after the accident.

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

Hayase's parents have filed a personal injury lawsuit in Utah's 3rd District Court against Mikuni and the travel companies tied to the trip. Attorneys for the family said 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 the pain and suffering, medical expenses, funeral expenses for their son and other damages. It contends that Mikuni, the Utah-based travel companies Canyon Transportation and Western Leisure Inc., and two Japanese tourism companies were negligent and failed to ensure the safety of travelers.

The first lawsuit stemming from the accident was filed in October. Court papers say Kei and Mai Maeda were celebrating their wedding anniversary when the crash left him with a broken neck and her with a punctured lung and an eye injury.