One of his victims has said his abuser should stand trial now.
A child protection expert has said he should not have been allowed to get away with the crimes, and that police had enough to pursue a prosecution.
"In this incidence you had an admission, so you didn't have... to worry that the allegation was old, and the evidence may be stale," said Jim Gamble, a former senior officer with the Police Service of Northern Ireland.
"You had a contemporary admission. And given that, I don't understand why he wasn't prosecuted."
'Legal system let me down'
Henry Clarke first came to the attention of police in 1982 when an investigation began into systematic abuse at the notorious Kincora boys' home in Belfast.
Some of the teenagers who had been abused at Kincora had come from Bawnmore, where they said they had also been sexually assaulted.
Belfast man Billy Brown, 61, was abused by Clarke at Bawnmore care home in Newtownabbey in 1968.
Mr Brown was just 12 years old and in care when Henry Clarke invited him to his family home, introduced him to his parents and then abused him while he slept.
He said Henry Clarke should be brought to justice no matter how long ago the abuse happened.
"The legal system let me down," he told BBC News NI.
"He should be brought to justice now. He should have faced the courts like everyone else. If I do something wrong I face the courts.
"At the end of the day, why should he not face the courts? I can't understand it. What was the reason they let him go?"
'Too long ago'
In 1985, Clarke admitted abusing two boys when taken in for questioning by police during a family holiday in Northern Ireland.
In a statement to police, he admitted to sexual touching a child. The indecent assault happened in 1968 - 17 years before his confession.
In spite of his admission, the Director of Public Prosecutions (DPP) ordered "no prosecution".
Asked why, the current Public Prosecution Service said that the DPP at the time considered the abuse had happened too long ago.
"The directing officer considered that given the time period which had elapsed (17 years) it would be inappropriate to pursue a prosecution," said a PPS spokesperson.
"The prosecutor in this case was following the applicable guidance at the time in the then DPPs' Office."
But leading Barrister Eugene Grant QC said the passage of time did not matter in this case.
"On any reading, the DPP decision not to prosecute here is devoid of any rationale or indeed any legal principle," he said.
"Simply to say a 17-year delay exists without more does not actually hold weight from a legal perspective."
Billy Brown said this reason did not make sense because two other child abusers who had sexually assaulted him in the late 60s had been tried and sentenced in the 1980s.
"The other ones, they went to jail, they done their bird," he said. "But he gets away."
After Henry Clarke returned to Canada in 1985, he wrote a letter to police in Belfast, confessing to another case of sexual abuse - this time against a resident from the Conway House children's home who was assaulted at a Boys Brigade camp in Newcastle, County Down.
"I wrote a letter to them and told them that I had missed telling them about this other boy and I felt at that point in time there would be consequences for my admission," he said.
But there were no consequences.
Given the state prosecutor's previous refusal to mount a case against Clarke, this time police did not even tell the DPP about this latest confession; the RUC said there should be "no further action".
A senior police officer wrote: "As the act admitted by Clarke is not punishable in law, there is no necessity to forward papers to the DPP."
But according to the PPS, the sexual touching of a child was, in fact, punishable in law at the time.
Barrister Mr Grant, who examined the papers in the case, said the act carried out on the boy was a crime and questioned the police's reason for not referring the case for prosecution.
"We have in the documentation a statement by a very senior RUC detective, who oversees the investigation, making it quite clear that, in his view, this is not an offence punishable by law," he said.
"That is quite clearly wrong and it does not make any sense, so in my view, the RUC decision not to send this file to the DPP fails."
Questions have also been raised over why the RUC did not alert the authorities in Canada to Henry Clarke's confessions of abuse.
In his letter to the RUC in 1985, he looked for an indication from the police as to whether they intended contacting the Royal Canadian Mounted Police.
A senior policeman from Northern Ireland concluded: "As Clarke has not been convicted of any offence, there is no obligation to notify the RCMP."
The PSNI said it was now reviewing how it shares information with the Canadian police.
Ch Supt George Clarke, head of the PSNI's Public Protection Branch, said: "It is noted that when the decision was taken not to inform RCMP, that was on the basis that Clarke had not been convicted of any offence, which may have been the relevant standard or requirement applicable then."
Since no one in Canada was made aware of Henry Clarke's admissions, he continued to live out his life without anyone in authority knowing about his confessions.
He pastored at four different churches before retiring.
'Your sin will catch you out'
Mr Gamble said it was a mistake that Canadian officials were not notified.
"I am not surprised that historically the police would have taken the position that in the absence of a conviction they wouldn't feel comfortable with sharing information," he said.
"I think that's an error of judgement.
"I don't know how many of us would have shared the information back then.
"The level of understanding and maturity around this was very low. Today I would expect that information to be shared."
When asked, Henry Clarke said he had never abused any children in Canada.
The abuse stopped when he left Northern Ireland, he said.
"I took the opportunity to start a new life and I went back to Bible college and did my training and from 1982 until now I've been a pastor," he told BBC News NI.
"I retired four years ago, but I've been a pastor and I've enjoyed doing what I'm doing."
Henry Clarke continues to live his life uninterrupted in Canada, where he has spent the last 30 years preaching from the Bible.
"As we say in the Church, your sin will catch you out," he said.
"In sitting here (talking to you) I am taking responsibility."