The Church of England ignored child sex abuse carried out by a former member of the general synod, a review has found.
Jeremy Dowling, a lay preacher, teacher and church employee, abused young boys in the 1970s and was jailed in 2015.
A review by the Diocese of Truro said several bishops were told about the abuse and did not take action.
It found there was a "probable misunderstanding" by church leaders over a decision not to prosecute him.
Dowling became a member of general synod in 1977 and was communications officer for the Diocese of Truro from 2003 to 2009.
The school where Dowling carried out the abuse cannot be named because of a risk of identifying the victims.
In September 1972 an unnamed canon, who was chairman of the board of governors at the school, wrote to the Right Reverend Maurice Key - Bishop of Truro from 1960-73.
'The devil is a master'
The canon said Dowling had admitted some sexual offences against boys and offered to resign.
In his response Bishop Key said it was "a tragedy for Jeremy Dowling" and "a real blow for the school and the church".
The bishop added: "The devil is certainly a master at attacking where he can do most harm."
In December 1972 the Director of Public Prosecutions decided not to prosecute Dowling.
The diocese report said the level of evidence needed in 1972 was "extremely high" but added the church had "its own responsibilities to judge such behaviour".
Successive bishops knew about the allegations against Dowling but did not launch any investigation or take any action, the review found.
In December 1986 an unnamed priest wrote to the Right Reverend Peter Mumford - Bishop of Truro from 1981-89 - referring to Dowling's "sadistic behaviour" while he was a teacher.
The Right Reverend Michael Ball - Bishop of Truro from 1990-97 - told the diocese he had been informed of the allegations but had not seen any need to take action as there had not been a prosecution.
His identical twin, former bishop Peter Ball, was jailed in 2015 for a string of indecent assaults on teenagers and young men.
A file found "in an unusual place" at the Bishop of Truro's residence in 2013 was passed to police and led to Dowling's prosecution.
'Culture of secrecy'
David Greenwood, chairman of campaign group Stop Church Child Abuse, said the problem persisted in the church because of "no external and independent oversight on issues of safeguarding children".
He said: "One cannot help think some child abusers are attracted to church organisations because they know they will receive favourable treatment if caught."
The diocese said it had "developed child protection and safeguarding policies" and now has "robust and well thought-out" processes in place.
On behalf of the diocese, Dr Chris Goldsmith, Bishop of St Germans, apologised "to anybody who has suffered as a result of past failings".
He said abusive behaviour "flourishes where there is a culture of secrecy" and said the diocese was now "committed to being transparent".