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An alert police officer who boarded a bus full of recent Utah high school graduates headed to Disneyland averted what could have been a deadly road trip after arresting the driver for suspicion of being under the influence of drugs, authorities said Friday.

"There's no other way to put it," said Cedar City police Lt. Darin Adams. "I really hate to think of what would have been. We may have been getting calls today that the bus had crashed and students were dead or injured."

About 100 students from Canyon View High School in southern Utah had just graduated Thursday night and boarded the charter bus for their senior trip, Adams said.

Parents and faculty members had asked police to bring a K-9 to the scene before the bus departed to check students' bags for drugs.

Officer Isaac Askeroth boarded the bus with his dog and another officer and immediately noticed driver Brandon Gillman, 30, of South Jordan, seemed suspicious, Adams said.

He was fidgety, began removing items from his backpack and stuffing them in his pockets as he tried to wander off the bus, he said.

"They saw some things that didn't add up and their instincts kicked in," Adams added.

The dog immediately alerted on the driver's bag.

Adams said the officer then found prescription pills, drug paraphernalia and what is believed to be cocaine in the backpack.

Gillman then failed a field sobriety test and was arrested on suspicion of possession of a controlled substance, possession of drug paraphernalia and driving under the influence, Adams said.

"This is a great day because we averted a tragedy," Canyon View High School Principal Richard Nielsen told the Deseret News. "In my mind, there's a strong likelihood that we (would be) having a mass memorial service instead of celebrating the accomplishments of these kids."

No telephone number was listed for Gillman, who remained jailed Friday. It wasn't immediately clear if he had an attorney.

Richard Maben, president of the charter bus company Utah Trailways, said Gillman started work in March and was a model employee. Maben said he passed drug tests and an extensive screening process, including a background check "with flying colors."

"In fact, he was one of our most complimented drivers. He was doing an excellent job," Maben said. "If this is true, I would certainly be shocked."

The students got on their way to Disneyland about an hour later with a new bus driver.