Robert Pimentel, L.A. teacher accused of molesting 20 children, had prior claims made against him

(CBS/AP) LOS ANGELES - Police say that an elementary school teacher accused of fondling as many as 20 of his female students had been accused of similar activity twice in the eight years before, but that the claims were mishandled by a principal.

Robert Pimentel, 57, is charged with 15 felony counts for allegedly touching students and a co-worker at George La Torre Jr. Elementary School between September 2011 and March 2012. 

Pimentel appeared in court Thursday and didn't enter a plea. His attorney maintained the 15 felony counts his client is facing are false.

"If you look at the record, before this, Pimentel has had a pretty exemplary life," said his lawyer Richard Knickerbocker. "He has no arrest record, for anything."

A previous report of sexual misconduct against Pimentel occurred four years ago at the school, and another complaint was made eight years ago at another elementary school where both a female principal and Pimentel had worked, said district Superintendent John Deasy

"My determination was that she was previously mishandling other complaints," Deasy said. "My intent was to fire them."

The district never got the chance because both Pimentel and the principal retired after the allegations surfaced last March.

"You can't fire someone who doesn't work for you," Deasy said.

Police said they will review the principal's failure to report those previous allegations.

It took nearly a year to bring charges against Pimentel and the investigation began just weeks after the arrest of another Los Angeles elementary school teacher, Mark Berndt, who has pleaded not guilty to 23 counts of lewd conduct involving students.

Following that scandal, the district mandated that parents be notified within 72 hours of a report of a suspected abuser, and that each case be reviewed by several human resources staffers to ensure it is reported to the Commission on Teacher Credentialing.

District officials vowed to investigate molestation claims and move quickly to remove suspected teachers from classrooms while investigations are ongoing, which apparently occurred in Pimentel's case.

Police were contacted in March by the parents of five students who said Pimentel had touched their children inappropriately. District officials immediately removed him from campus and notifications were sent out.

More than 70 interviews were conducted during the police investigation, and Los Angeles police Capt. Fabian Lizarraga said 20 female students are believed to have been victimized. In addition, a female teacher who complained that Pimentel had inappropriately touched her, police said.

The alleged abuse occurred in Pimentel's fourth-grade classroom during school hours and, in some cases, was witnessed by other students, Lizarraga said. The sexual abuse involved fondling over and underneath clothing, he said.

"These were some really alert parents knowing their kids and noticing subtle changes in their personalities," Lizarraga said.