Montreal police chief Marc Parent said a retired police officer alleged to have leaked the names of informants to the mafia was a 33-year veteran of the force.
Parent said charges against the officer are pending, and that authorities are taking the allegations against him seriously.
According to information obtained by Radio-Canada, the officer allegedly tried to sell a list of informants to the mafia for a six-figure sum.
Police found out about the leak through a wiretap investigation in April 2011. The information gathered led to the officer's arrest in October 2011.
Parent said the retired officer was part of the special investigations unit as an intelligence officer.
"The individual has been working for us for 33 years so he knows all the techniques," Parent said. "He knows all the police officers that could be investigating such a crime so it is very complex."
Some reports suggest a few names on the confidential list were leaked, but Parent insisted those sources are not at risk.