A teacher from Redwood City who previously worked in Palo Alto has been arrested on suspicion of engaging in sex acts with a juvenile, according to the San Mateo County District Attorney's Office.

The county charged Dawn Giannini, 49, with 24 felony counts, including lewd acts with a child and sexual penetration with a foreign object, during a court appearance on Thursday, Oct. 25, according to San Mateo County District Attorney Steve Wagstaffe.

Giannini was arrested on Oct. 18.

A Woodside High School student alerted the school's principal of several videos of a female classmate engaged in sexual acts with Giannini, Wagstaffe said. The videos were on the pornography website Pornhub. Woodside's principal immediately contacted police, Sequoia Union High School District officials told The Almanac.

The videos were shot from November 2014 to November 2015 in Redwood City and Santa Cruz County, when the victim was 14, according to the district attorney's office. The victim is related to Giannini, Wagstaffe said.

Giannini taught at schools in Redwood City and Palo Alto. She was substitute teaching when she was arrested, Wagstaffe said. He did not know the name of the school where she most recently worked.

Giannini started as a special education assistant and substitute teacher for the Redwood City School District in 2007, according to Jorge Quintana, the district's director of communications. Superintendent John Baker emailed parents about the charges on Thursday, Oct. 25, and indicated that the district will never employ Giannini again. Baker wrote that the allegations are "truly heartbreaking," adding that the district did a background check of Giannini when she was hired, which she passed.

"The police department tell us that the conduct for which she has been charged has no connection to a school setting or her former status as a school employee," Baker wrote.

Giannini worked at schools throughout the district. Officials did not say when she last worked for the district.

Giannini spent the 2015-16 academic year at St. Elizabeth Seton School in Palo Alto, where no known allegations were made against her, according to the Diocese of San Jose.

St. Elizabeth Seton parents were informed of Giannini's arrest in writing, according to Principal Evelyn Rosa.

Giannini remains in custody on $1.75 million bond, according to Wagstaffe. The case has been continued to Nov. 5 for plea entry and to set a preliminary hearing date.