CUPERTINO -- A 16-year-old Monta Vista High School student has admitted to authorities that he threatened a bomb attack on a teacher at the school, which had prompted its closure on Thursday and that of a nearby elementary school -- even as the teacher remained under protective custody, according to the Santa Clara County Sheriff's Department.

Lt. Rick Sung on Saturday night said the student, whose identity is being withheld because he is a juvenile, was arrested at his Cupertino home at 5 p.m. Friday. County officials on Saturday night said the youth remains in custody.

Sung said "several pieces of evidence'' led to the teen's arrest, but he would not elaborate on what that was. The teen confessed to making the threat, according to Sung. The boy's father also was present during the arrest, he said.

"I credit the deputies for their tenacious effort,'' said Sung, who said the youth was booked on charges of criminal threat against a teacher, making a bomb threat, as well as several charges involving disrupting school business.

Sung said sheriff's deputies consider all threats against schools, school officials and students to be serious, because of "all the violence that has taken place on school grounds'' over the years. Sung said investigators who worked on the case Friday were thinking about the gunman in Connecticut who fatally shot 27 people, including 20 children, before killing himself.

Sung said he could not confirm if the Monta Vista student knew the teacher that the teen had allegedly threatened, nor would Sung disclose any motive behind the threat.

The sheriff's department had been alerted at about 6:40 a.m. Thursday to the threat, after San Jose police alerted county authorities of the discovery of graffiti at Lynbrook High School that claimed there was a bomb at Monta Vista. The graffiti threatened a Monta Vista teacher by name.

Bomb-sniffing dogs swept the campus at around 7 a.m. Thursday, the same time the Monta Vista principal sent out an alert to students and parents announcing that school would be closed for the day.

Sung said more than a dozen students and adults, including teachers at Monta Vista, were interviewed during the course of the investigation and that deputies were able to narrow down a small group of "people of interest'' to the one suspect.

"Evidence linked that particular student to the crime,'' Sung said.

He declined to comment on students' claims to a Mercury News reporter on Thursday that the teacher in question had been threatened earlier last week, but said that the teacher was given protection because the threat singled someone out.

Contact Tracy Seipel at 408 275-0140.