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WILMINGTON, Calif. (KTLA) — A former elementary school teacher with the Los Angeles Unified School District has been arrested in a sexual abuse case involving at least 20 children and one adult.

Robert Pimentel, 57, who taught at George de La Torre Jr. Elementary School in Wilmington, pleaded not guilty Thursday to eight counts of continuous sexual abuse and seven counts of lewd acts on a child.

Police launched an investigation last March after several fourth grade girls said they had been inappropriately touched.

Some of the children told their parents they had been abused, and the parents then altered the LAPD’s Harbor Division.

Prosecutors have filed 15 charges against Pimentel involving a dozen of his alleged victims.

The charges involve sexual abuse and lewd acts on a child and cover the period from September 2011 to March 2012, according to court records.

Authorities said the teacher is suspected of inappropriately touching children under and over their clothing.

Pimentel is suspected of victimizing and additional eight children and an adult co-worker.

Of the 20 alleged minor victims, 19 were students at the school, said LAPD Capt. Fabian Lizarraga. Detectives discovered the other child as they gathered evidence.

LAUSD Superintendent John Deasy said both Pimentel and the school’s principal were removed from their positions when the district learned about the allegations in March.

Deasy said he removed the principal after learning she had received an allegation about the teacher four years ago but took no action.

He said the teacher’s file “contained notations of suspected misconduct along the lines for what he was later charged with, which was inappropriate touching of a student.”

The district said parents were informed within 72 hours after Pimentel was removed from the campus. The California Commission of Teacher Credentialing was also promptly notified.

District officials prepared a “notice of termination” for Pimentel and the principal, according to Deasy.

They had planned to present it to the Board of Education in April 2012, but both retired before the board meeting. Because they retired before the district took action, they will get their full pensions.

“People who commit acts like this should be terminated, and that termination should be made easy,” Deasy said on Thursday morning.

“We should not have cumbersome state laws around this, and you should be able to fire someone even if they choose to retire.

“We notified the office of teacher credentialing the very day of the action. To my knowledge, I don’t think his credential has ever been revoked, either.”

Pimentel, who lives in Newport Beach, had been a teacher with the district since 1974.

The LAUSD, which is the nation’s second largest school district, has been rocked in recent months by allegations of sexual misconduct involving teachers and students.

Former Miramonte Elementary School teacher Mark Berndt, 61, was arrested last January after photos surfaced that show students blindfolded and being fed cookies allegedly tainted with semen.

He has pleaded not guilty to 23 counts of lewd conduct and is awaiting trial. The district is facing nearly 200 molestation and lewd conduct claims related to Berndt’s alleged wrongdoing.