REDWOOD CITY (Map, News) - The English teacher accused of secretly videotaping girls in a Mills High School bathroom also peeped on students using a hidden camera stashed under his classroom desk, prosecutors said Tuesday.

David Lista, 35, had stored well more than 20 images of girls he reportedly filmed in a bathroom stall onto a school-issued computer, Chief Deputy District Attorney Steve Wagstaffe said.

On a separate computer seized at his Belmont home, Lista had allegedly saved another 20 inappropriate images of students he had filmed during class — from a camera pasted under his desk, Wagstaffe said. His home computer also contained hundreds of other pictures and videos accessed from a wide-reaching child pornography trade, investigators said.

Lista pleaded not guilty to the charges Tuesday in a South San Francisco courtroom. He was officially charged Friday for the alleged bathroom tapings, nearly a month after police executed a search warrant on his residence. FBI analysts spent that time examining the computers the teacher had used, partly trying to determine if any of the improper school footage had ended up on the Internet.

“We have nothing that would lead us to believe that any of the pictures involving girls at the school were circulated or distributed,” Wagstaffe said.

Lista, a Mills teacher since 2002, remains on paid administrative leave until the San Mateo Union High School District board meets next week to decide whether to fire him, district Superintendent David Miller said. He said the district did not want to take action until Lista was officially charged.

Miller said he was saddened by news of the alleged tapings, saying all teachers in the district were personally hurt that the children “were betrayed that way.”

“Those kids trust us,” Miller said. “There’s no bigger letdown than that. All the teachers feel hurt by this ... I know the military feels that way when one solider goes bad.”

Miller said the girls’ bathroom where the filming allegedly took place has since been repainted and that broken tiles were replaced.

At the time of his arrest, Lista reportedly confessed to police that he had videotaped the bathroom before Christmas and again on Valentine’s Day, a school district official said.

Lista was previously out on $10,000 bail after being arrested March 6 for a misdemeanor drug charge. Bail was raised to $125,000 on Tuesday at the request of prosecutors. A preliminary hearing was scheduled for July 29, Wagstaffe said.

maldax@examiner.com