The document that was allegedly concealed from Tremblay and the city's executive committee was completed in February 2004. It contained information about construction contracts that were inflated by 30 to 40 per cent due to collusion in the industry.
Montreal Mayor Michael Applebaum said the comptroller's investigation into the document holds evidence pertinent to ongoing police investigations.
He said the city would be unable to look deeper into the issue.
Applebaum refused to give details on the content of the comptroller's report.
"We will send this dossier over to UPAC because they have more ability to investigate and question the individuals to get a more clear understanding of what happened," said Applebaum.
On Tuesday, Alain Bond, the city's comptroller, said former city director general Robert Abdallah and former head of the executive committee, Frank Zampino, kept the 2004 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 inflated costs 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.
Bond said he gathered various documents and talked to many people or his investigation but would not confirm whether he spoke to Abdallah or Zampino.
Vision Montréal leader Louise Harel said she supports Applebaum's decision but said it's a sign Montreal should do like Toronto and have an ethics commissioner with more power to investigate similar cases.
"The City of Toronto, you count on an ethics comissionner with real powers to inquire and to make sanctions against elected officials or against firms who have contracts with the city, and we don't have the same here," she said.