As many as 263 youth may have been sexually abused by former Saint John police officer Kenneth Estabrooks, during a three-decade period dating back to the 1950s, a private investigator announced on Monday.

It could be one of the worst cases of sexual abuse in Canadian history, according to a Halifax lawyer.

"If what we're learning today is true, Estabrooks is now probably the most prolific serial sexual abuser in Canadian history," said John McKiggan, who is on the verge of filing a class action lawsuit on behalf of Estabrook's victims.

"One just has to wonder how that could have gone on for so long," he said.

Private investigator Dave Perry, whose Toronto-based firm Investigative Solutions Network Inc. was hired by the City of Saint John to look into complaints about the late Estabrooks, said the former officer was an abuser of devastating proportion, affecting generations.

"The trajectory of the investigation has reached an almost unprecedented level with regards to both the historical nature, as well as the number of identified and potential victims," said Perry.

"The investigation to date, has revealed a magnitude of victimization of children typically only uncovered from within institutional settings."

Fifty-three people have come forward so far, alleging they were sexually assaulted as children by Estabrooks, said Perry.

Another 33 suspected victims have since died, while six other people said Estabrooks had attempted to abuse them, Perry said.

But the total number of victims could climb as high as 263, he said.

The remaining individuals who were exposed as children to Estabrooks during his policing career have not yet been located, he said.

Many were victimized repeatedly over weeks, months, and for some, over a period of many years. —Laura Bradbury, private investigator

The alleged victims ranged in age from six to 19, and were primarily boys, said Perry.

"Many were victimized repeatedly over weeks, months, and for some, over a period of many years," said fellow investigator Laura Bradbury.

Those who are still alive now range in age from their 40s to 60s, they said.

Estabrooks, a former sergeant, was found guilty in September 1999 of indecent assault against four children, in cases dating back to the 1950s. The abuse included fondling and oral sex.

Initial investigation substandard, unprofessional

Estabrooks had admitted in 1975 to sexually abusing children, but he wasn't charged or fired. Instead, he was transferred out of the police department into the city works department, where he was in charge of tire maintenance for city vehicles until he retired.

It was only in 1997, after new complainants came forward, that another investigation began, resulting in his conviction.

In 1999, the New Brunswick Police Commission found the original investigation was substandard and that the police force acted unprofessionally in "allowing a serious sex offence to go unpunished" so that "he continued to sexually assault children."

Estabrooks died in 2005.

Saint John Mayor Mel Norton said the city is committed to seeing the investigation through and is footing the bill, which has reached $400,000 so far.

"Our main priority has remained on those affected — reaching out, hearing their stories and offering them free, confidential counselling services that will hopefully provide them a chance at a more peaceful future," he said.

Norton also made a direct appeal, calling on any other victims or anyone with information to come forward by calling 1-866-790-4764.

The city hired Investigative Solutions Network Inc. in August 2012 for $100,000 to look into at least one other historical complaint against Estabrooks.

In November, the city revealed there were 12 new alleged victims and allocated another $100,000 to probe additional complaints.

Last week, council approved spending an additional $100,000 on the investigation.