A Catholic school principal and a fellow teaching nun were caught pilfering "a substantial amount" of money from school coffers in a quiet, years-long theft in Southern California, officials said Friday.

Parishioners of St. James Catholic Church in Redondo Beach and parents of kids at its elementary school were alerted in a letter this week about theft allegations against Sisters Mary Margaret Kreuper and Lana Chang.

"It is with much sadness that I am informing families of the St. James School that an internal investigation has revealed that, over a period of years, Sister Mary Margaret Kreuper and Sister Lana Chang have been involved in the personal use of a substantial amount of School funds," according to a letter from Msgr. Michael Meyers.

"This matter came to our attention during financial reviews in connection with the change in leadership at our School. Other staff persons were not implicated or responsible."

Kreuper and Chang both retired at the end of this past school year. Kreuper was principal for 29 years while Chang was a teacher for about 20 years and had also recently served as vice principal, according to a spokesman for the Los Angeles Archdiocese.

A Feb. 4 church newsletter had heralded Kreuper's retirement, listed her work phone number and urged parishioners: "Take time to thank her for her generous service."

Last week, the school alerted police in Torrance, where the sisters' elementary school is located, about the possible theft, according to Sgt. Ron Harris.

Church officials don't want the nuns criminally prosecuted but police will still follow up on the case and present findings to the Los Angeles County District Attorney's Office.

"We were made aware that they're not desirous of a prosecution, " Harris told NBC News on Friday. "We’ll look at all the facts that ware given to us and we’ll consult with the DA."

Kreuper, Chang and their St. Joseph of Carondelet order are cooperating in the ongoing internal probe, with plans to make "full restitution," according to Meyers.

"Sister Mary Margaret and Sister Lana have expressed to me and asked that I convey to you, the deep remorse they each feel for their actions and ask for your forgiveness and prayers," according to Meyers.

"They and their Order pray that you have not lost trust or faith in the educators and administrators of the school."

The disclosure stunned parents who knew Sister Mary Margaret and Sister Lana as tough but well-liked educators.

"This is such a huge, huge shock, really disappointing," said Viveca Tokatlian, whose son is now a senior at the University of San Diego and was once student in Chang's eight-grade class. "They were just such staunch defenders of moral fortitude, they were really tough on the kids."

The nuns lived in modest church housing, drove old cars, wore basic clothes and did nothing that would hint of enjoying extra cash, according to Tokatlian.

The nuns could not be reached for comment on Friday through publicly listed phones numbers for them and it was unclear if they had lawyers.

“Unfortunately, this is what now what their legacy is going to be — it’s not going to be all the good things they did,” said Tokatlian, 53.