LOS ANGELES (CBSLA.com) — Complaints of misconduct against a Los Angeles Unified school teacher who was convicted last year of spoon-feeding his semen to his students first surfaced over 30 years ago, according to a report Friday.

KNX 1070’s Jon Baird reports parents of students at Miramonte Elementary were largely upset after learning that school officials faced a civil lawsuit that claimed Mark Berndt dropped his pants on a school field trip in 1983.

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According to court documents, LAUSD officials knew of allegations over inappropriate behavior by Berndt about 10 years earlier than the disrict previously claimed, The Los Angeles Times reported.

A memo cited by The Times reportedly showed a handwritten note from Berndt apologizing “for any embarrassment” caused by the incident and thanking the school’s principal at the time for his support.

The memo included a line apparently from Berndt that read: “I did learn at least one thing for sure! Not to take students to the museum while wearing baggy shorts!” according to The Times.

Other students claim they told school officials in 1992 that Berndt would masturbate in class, The Times reported.

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Berndt, 63, pleaded not guilty in Nov. 2013 to 23 counts of lewd acts on a child for crimes he allegedly committed between 2005 and 2010. He is accused of taking photos of students while they were bound and gagged in his classroom.

Some photos featured cockroaches being placed on students’ faces, while others depicted them being spoon-fed a milky-white substance that tested positive for Berndt’s DNA.

Berndt, who was arrested in January 2012, was sentenced to 25 years in prison.

Parents at Miramonte were stunned to learn the district may have known about Berndt’s behavior and failed to let parents know.

“I think it’s so messed up, because they knew already,” said one father.

“They should’ve told the parents about it,” another parent said.

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An LAUSD spokesperson would not comment on any of the details of the memo.