The city of Saint John hired Toronto-based Investigative Solutions Network to look into further allegations about former police sergeant Ken Estabrooks, who died several years ago.
He was convicted in 1999 of indecent assault against four young people between 1957 and 1982 and received a six-year prison sentence.
David Perry of Investigative Solutions Network said Monday the total number of victims might be higher.
"There are a lot of people we haven't spoken to yet but the list of potential individuals is now at 263," he said in an interview.
"I suspect a large number of them were victims of Ken Estabrooks but there may be a significant number who tell us no, it didn't happen to me."
Perry said 33 people on the list are dead but other people provided their names as possible victims.
Allegations against Estabrooks first surfaced in 1975 when he was a 22-year veteran of the Saint John Police Force.
Although he resigned immediately when confronted with the allegations of two teenaged boys, no charges were laid.
After new complainants came forward in 1997, another investigation began that ended with Estabrooks being convicted of indecent assault on four of his six accusers.
None of the new allegations have been proven in court, but the city is offering counselling services to anyone who alleges they were a victim.
Perry said most of the 53 people have taken the counselling that was offered to them.