One cover-up involved a Marist Brothers principal in Sydney, who was aware that now-notorious child predator Brother Francis "Romuald" Cable was abusing boys, but failed to report him to police.

Cable instead went to Newcastle, where he molested another 11 children before leaving the order to teach at St Edmund's between 1979 and 1989.

Fairfax Media has also established that the Christian Brothers, who then ran St Edmund's, became aware of a complaint against one of their NSW brothers, but sent him to Canberra regardless, allowing him to allegedly abuse another boy.

The Christian Brothers concede their past handling of such cases was flawed and that "what happened 25 years ago is not what the community or we would accept today".

The Marist Brothers say the Sydney principal never reported Cable's abuse to his superiors, and that the order's leadership did not become aware of any complaint until 1993, when his teaching career was over.

Cable hunted boys with an unnerving depravity and audacity before he moved to the ACT, molesting or raping at least 19 students at three Marist schools in the 1960s and 1970s.

Labelled one of NSW's worst Catholic school paedophiles, he twisted religious doctrine and used his authority to manipulate victims, many of whom were troubled or from broken families.

He molested boys in his office, on excursions, behind his desk as fellow students sat nearby, and at the local swimming pool.

"You won't say anything to anyone," he told one boy. "You are not Catholic and have the mark of the devil on you."

The same child was later beaten mid-rape to stop him screaming out in pain.

Afterwards, the boy asked Cable "what have you done to me?", prompting the brother to hit him again, tell him to "remember our little secret", and bless him in Latin.

Cable's crimes were only recently reported publicly. He was sentenced last year to 16 years in jail for abusing 19 students over 15 years. Now 84 and frail, he is likely to die before he is eligible for release.

There is no evidence Cable abused children at St Edmund's.

However, Fairfax Media can reveal that Cable could have been stopped 12 years before he even arrived in the ACT.

A principal at a Marist school in Sydney, St Gabriel's in Pagewood, was told Cable was abusing boys as early as 1967.

One victim told police in 2013 that the principal came to his parents' home, asked him whether he had been touched indecently, and then assured him and his father that Cable had been "spoken to" and would be moved.

The principal failed to report the allegations to the police, and Cable was sent to a school in Newcastle, where he abused a further 11 boys over the next eight years.

Strangely, a detailed, official history of the Marists' Hunter Valley schools, published in 1998, omits any reference to Cable, despite his decade of service there.

But the Marists say the St Gabriel's principal never took the matter to the order's leadership when he learned Cable was abusing children in 1967.

"In saying that, in no way do we contradict the witness statement made in 2013 in relation to events in 1967, and we accept the witness may have told the principal at that time," Marist Brothers Australia said in a statement.

"However no record, statement or summary of that allegation was ever forwarded by the principal to the Marist Brothers."

The Marist Brothers said they first received a complaint about Cable in 1993, well after he had finished teaching but decades before police began investigating him. They had no cause for concern when Cable left the brotherhood and moved to Canberra.

The Marists also said the 1993 complaint could explain why Cable was not mentioned in the history of Hunter Valley schools published five years later.

"It is possible that his name was deliberately omitted to spare victims unnecessary discomfort."

The Christian Brothers, who then ran the ACT college, say they immediately searched their records mid-last year after learning of his prior abuse in NSW, but found no complaints.

"We strongly urge The Canberra Times or any person who may hold any evidence of criminal conduct at the school to refer that to the police for the proper investigation," the brothers said in a statement.

Cable was a lay teacher at the college, swapping his first name Francis for "Rom", an abbreviation of the saintly moniker he took as a Marist brother.

Fairfax tracked down 10 of Cable's St Edmund's colleagues from the 1980s and told them of his history.

Many were shocked, saying they knew nothing of his past abuse nor of any complaint about him while he taught in Canberra. Several said the headmaster at the time would not have hired Cable had he known.

One clearly remembered Cable for his "ridiculous" contempt for the children. "He just had that real sense of hatred that kind of shocked me."

Do you know more? email christopher.knaus@fairfaxmedia.com.au

Roughly 20 of Cable's ex-students from St Edmund's were also found. Some described him as a cruel man, who picked on children and appeared to enjoy corporal punishment, while others said he was an unremarkable teacher who had not caused problems.

"My experience with him was horrible. He was not a nice person," one said.

It is understood ACT police have not received complaints about Cable's time at St Edmund's.

But clergy-abuse survivors have expressed concerns about his decade here.

Bob O'Toole is a co-founder of the Clergy Abused Network. He was abused by another Marist teacher, Brother Leon Mackey, at the same Newcastle school where Cable preyed on children.

Mr O'Toole said Cable's move away from the Marists would be unlikely to have changed his behaviour.

"I'd be extremely surprised. These people don't just get to 1979 and suddenly stop."

A second brother was also sent to St Edmund's in disturbing circumstances.

The man, who cannot be identified for legal reasons, was teaching at Christian Brothers schools in NSW before he came to the ACT in 1978.

A child-abuse allegation had been made against him in NSW. Despite being aware of that complaint, the Christian Brothers allowed him to move to St Edmund's to teach until 1983.

"We acknowledge that this appears to have occurred notwithstanding a previous complaint that resulted in the later settlement of a civil claim," the order said in a statement.

He was then accused of abusing a boy at St Edmund's, which also led to a civil claim and settlement.

The brother was then moved out of the ACT, and has since been accused of more child sexual abuse after his time at St Edmund's.

Those allegations are currently before a court interstate, restricting what the Christian Brothers can say about the brother.

But the order did say its past handling of such cases had been flawed and offered its "unreserved apology" to any student who suffered abuse.

"Sadly, it has been the ongoing learning from our own work and that of the royal commission that poor practices in the past have failed to deliver acceptable outcomes," it said.

ACT Policing's child-abuse taskforce, Operation Attest, can be contacted via 131 444.