The nature of the earlier probe of Mark Berndt, a 30-year teaching veteran, was not disclosed, but the decision to drop the case was made by the district attorney on February 23, 1994, the prosecutor said in a written statement.
"After careful evaluation, it was determined that the evidence was insufficient to prove a crime occurred," the statement said. "A prosecutor cannot ethically file criminal charges if the evidence fails to meet the standard of proof beyond a reasonable doubt."
Berndt, 61, faces more recent allegations. He sits in jail with his bond set at $23 million over 23 felony counts of lewd acts on a child.
Investigators waited more than a year before arresting Brendt, a teacher at Miramonte Elementary School in south Los Angeles, after finding bondage photos apparently taken in his classroom, but a sheriff's sergeant says, "We always had our eyes on him."
Although the probe began in October 2010, when a drugstore photo processor called police, Berndt was not taken into custody until this week. He was removed from the classroom in January 2011.
At least 23 children in the images have been identified, while another 10 are unidentified, said Los Angeles County Sheriff's Sgt. Dan Scott, who supervised the investigation.
The 400 photographs collected by investigators show children blindfolded, with tape over their mouths, and some with suspected semen-filled spoons at their mouths, Scott said.
Some photos show female students with "what appeared to be a blue plastic spoon, filled with an unknown clear/white liquid substance, up to their mouths as if they were going to ingest the substance," authorities said.
The probe began when a CVS drugstore photo technician in the South Bay area of Los Angeles County told the Redondo Police department about finding disturbing images of blindfolded children in a processing order, Scott said.
Redondo police investigators called the Los Angeles Sheriff's Department on December 2, after determining the photos were taken in Berndt's classroom.
CLICK HERE FOR FULL CNN STORY