When a co-worker caught McKinley High School employee Gregory Keau having sex with a "special needs" student this year, Keau repeatedly asked the co-worker not to report him, according to court testimony yesterday.

Keau said, "I can explain" and "Can we talk?" according to Jonathan Cariaga, who worked alongside Keau for more than two years at McKinley.

"I said 'No, there's nothing to talk about,' " Cariaga said.

Cariaga testified he took the 17-year-old victim, a "mildly mentally retarded" girl from the Marshall Islands, out of the storage room where she had been assaulted. She told him that Keau had made her perform oral sex on him once before at the school in 2007.

Cariaga immediately informed school officials and police.

Yesterday, Keau was sentenced to 10 years in prison by Circuit Judge Michael Town.

Keau "took advantage of the disadvantaged," Deputy Prosecutor Thalia Murphy told Town.

She asked Town to sentence Keau to 22 years in prison for his crimes.

Keau apologized to his victim's family and to his own family, saying he was "extremely sorry for my illegal, immoral and unethical actions."

His lawyer, Lee Hayakawa, asked Town to sentence the 30-year-old defendant to probation.

Keau has "a teachable spirit" and is "worth saving," Hayakawa told the judge.

But Keau committed "an egregious breach and betrayal of trust," the judge said in ordering him to be locked up for 10 years.

"You crossed the line," Town said. "What were you thinking?"

The victim's grandmother, who has adopted the girl as her daughter, addressed the court in halting English, saying the victim "is not the same girl as she was before."

The victim "has scary nightmares," she said.

"My husband and I try very hard to help her in every way we can but it's very hard."

Murphy told Town that in addition to assaulting the student, Keau infected the victim with a sexually transmitted disease.

Murphy noted that Keau had a minor criminal record when he went to work as an educational assistant at McKinley and wondered how he could have been hired.

He was convicted of misdemeanor charges of assault and violation of a protective order and had received a deferred finding of guilt after pleading no contest to a disorderly conduct charge, Murphy said.

Keau's mother, also an educational assistant at McKinley, spoke on her son's behalf and said she helped him get the job at the school.

"I'm the one that got him hired," said Cherylann Makilan.

"I'm happy he took responsibility" for his crimes by pleading guilty, she said in court.

Prosecutor Murphy praised Cariaga for immediately reporting Keau's conduct.

Cariaga said he was angry and disgusted by Keau's conduct.

"I worked with him," he said. "He was my friend."

He testified that he looked for Keau and the victim when they didn't appear with other special-education students and teachers in a kitchen area of the school May 16 of this year.

He discovered them in a storage room, with the student on her knees in front of Keau.

After separating the pair and moving the student to a safe area, Cariaga said, he again spoke with Keau.

"He said he wouldn't do it again; he said it was the first time," he related. "The victim had already told me how many times it happened."

Keau told Cariaga that he had nearly completed training to become a Honolulu firefighter and that if Cariaga reported him, he would lose both his school job and his future as a firefighter.

"I told him he needed help," Cariaga said.