The internal study, published in February 2004, found construction contracts were inflated by 30 to 40 per cent due to collusion in the industry.
Alain Bond, the city's comptroller, said former city director general Robert Abdallah and former head of the executive committee, Frank Zampino, kept that report under wraps.
The city's current director general Guy Hébert, who handled the file at the time, said he handed the study over to Abdallah.
Abdallah denied hiding the report.
He said the executive committee must have known about the cost inflation detailed in the report because he was asked to approve a cost analysis contract with a private firm a few months after the report's publication.
On Monday, Applebaum said Tremblay and other officials were kept in the dark on the issue of construction costs.
"It is clear for me, when I read the comptroller's document, that this study was never handed to mayor Tremblay or other elected officials like Alan De Sousa, Helen Fotopoulos. For me, it's clear they did not know about this report," said Applebaum.
Bond's findings will be presented to the executive committee Wednesday.
In October, former construction boss Lino Zambito told the Quebec corruption inquiry that Abdallah was participating in a kickback system.
Abdallah denied all accusations.
Former executive committee chair Frank Zampino was arrested and charged with fraud, conspiracy and breach of trust last May. Investigators allege he was the mastermind behind a scheme to favour one company in the awarding of a $300 million municipal contract.