When faced with allegations of sex abuse against one of its bishops, the Church of England "colluded and concealed rather than seeking to help those who were brave enough to come forward," the church's leader acknowledged Thursday.

"For the survivors who were brave enough to share their story and bring Peter Ball to justice, I once again offer an unreserved apology," Justin Welby, archbishop of Canterbury, said in a statement. "There are no excuses whatsoever for what took place and the systemic abuse of trust perpetrated by Peter Ball over decades."

Welby was responding to the findings of an independent investigation into how the church handled the allegations against Ball, a former bishop who pleaded guilty in 2015 to indecent assault against young men. That report, also released Thursday, found that Ball "abused many boys and men over a period of twenty years or more."

"That is shocking in itself but is compounded by the failure of the Church to respond appropriately to his misconduct, again over a period of many years," Moira Gibb, who led the investigation, said in the report. "Ball's priority was to protect and promote himself and he maligned the abused. The Church colluded with that rather than seeking to help those he had harmed, or assuring itself of the safety of others."

The report goes on to lay out its extensive evidence against the 85-year-old Ball, who served a prison sentence of just over a year and was released on probation in February. The "harrowing" report — in Welby's words — details how investigators say Ball would use the trappings of his office to his advantage:

"He had a well worn 'modus operandi', in which he would target and groom boys and young men. His abuse was charged with religious intensity. The men we interviewed spoke of how he 'exploited the significance, particularly within the Anglo Catholic tradition, of ritual'. For Ball religious rites became 'a mask for abuse, and theology (was) used as a way of justifying abuse'. The evil of what he did was 'compounded by his message that this made the victims more special and more holy'."

But nearly as damning is the report's assessment of Lord Carey, former archbishop of Canterbury. Investigators say Carey was warned repeatedly about Ball's actions but failed to act on them appropriately.

What's more, the report states, "Lord Carey played the lead role in enabling Ball's return to ministry" after Ball was arrested on suspicion of indecent assault in the early 1990s — "that was not a decision taken by anyone else."

"This is inexcusable and shocking behaviour and although Dame Moira notes that most of the events took place many years ago, and does not think that the Church now would conduct itself in the ways described we can never be complacent, we must learn lessons," Welby said in his statement.

According to Welby, that includes endorsing the report's 11 recommendations centered on supporting survivors and reinforcing disciplinary measures.

"For the survivors, it may feel this is all too late," Peter Hancock, the church's lead bishop on safeguarding, said in a statement. "I am personally aware from my meetings with individual survivors in the course of my work that they live with the effects of this abuse for their whole life. I once again offer them my wholehearted apology."

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