The last thing an America bishop wanted to see was a letter from the relentless A.W. Richard Sipe, who spent more than a half-century studying the sexual secrets of Catholic clergy.

As a psychotherapist, his research files included hundreds of thousands of pages of church reports and court testimony. He estimated that he had served as an expert witness or consultant in 250 civil legal actions.

As a former Benedictine monk and priest, his private files included notes from years of work at the Seton Psychiatric Institute in Baltimore, where he counseled legions of troubled priests sent there by bishops.

"Sooner or later it will become broadly obvious that there is a systemic connection between the sexual activity by, among and between clerics in positions of authority and control, and the abuse of children," he wrote, in a 2016 letter to his local shepherd, San Diego Bishop Robert McElroy.

"When men in authority -- cardinals, bishops, rectors, abbots, confessors, professors -- are having or have had an unacknowledged secret-active-sex-life under the guise of celibacy an atmosphere of tolerance of behaviors within the system is made operative."

Sipe, 85, died on Aug. 8, even as journalists around the world produced -- often with direct links to his work -- yet another wave of news about alleged sins and crimes committed by priests and bishops. The bottom line: Sipe was a critic of the church establishment whose work was impossible for liberal or conservative Catholics to ignore.

"He was the one who -- because of his unique background -- had first-hand knowledge of the psychosexual problems in the clergy," said Leon J. Podles, a conservative Catholic scholar with years of experience as a federal investigator.

Sipe "saw what others ignored, which was that many priests and bishops were hiding secrets. If someone tried to take a stand about sex abuse, someone else would say, 'But what about your boyfriend or your girlfriend?' … He saw how this produced a code of silence, like the secrets that often surround incest, generation after generation."

In his letter to McElroy, which has been posted online, Sipe noted: "A serious conflict arises when bishops who have had or are having sexually active lives with men or women defend their behavior with denial, cover up and public pronouncements against those same behaviors in others. Their own behavior threatens scandal of exposure when they try to curtail or discipline other clerics about their behavior even when it is criminal as in the case with rape and abuse of minors, rape, or power plays against the vulnerable."

Sipe stood by his estimate that 6 percent of Catholic clergy have some history of sexual abuse, with some dioceses and religious orders seeing figures nearing 25 percent. And in his books -- "A Secret World" in 1990 and "Celibacy in Crisis" in 2003 -- he presented evidence backing this claim: "At any one time no more than 50 percent of priests are practicing celibacy."

The bottom line: "Sexual violation within the RC clergy is systemic. I say that on the basis of observation and scientific conclusion. And I say that with empathy and concern," wrote Sipe, who left the priesthood in 1970 to marry Marianne Benkert, a psychiatrist and former nun.

The 2016 McElroy letter contained page after page of material drawn from court testimonies and documents linked to financial settlements with victims -- including old reports about Archbishop Theodore McCarrick, who recently resigned as a cardinal after a storm of new allegations about his abuse of boys, young men and seminarians.

This material is often public record, but the X-rated details are rarely included in news reports -- such as testimonies about sacrilegious rites performed during and after sexual acts. One Maryland boy testified that his attackers displayed their erections and told him, "See what you have done."

Podles included scores of similar cases in his scathing book, "Sacrilege: Sexual Abuse in the Catholic Church." He said it's hard to imagine the horrors in Sipe's private files, "which I am sure he had destroyed." Sipe's files of public records went to BishopAccountability.org.

Sipe was "dealing with realities that were truly demonic," said Podles. "What can you say when men dress boys up as Jesus and then rape them? … Sipe knew all of the layers of this crisis and he never stopped fighting."