A retired Montreal detective who had three decades of police service is under investigation for allegedly trying to sell a list of informants to the Mafia.

The former officer, who had the rank of detective-seargent, was among the privileged few on the force who had access to such sensitive information, said police investigator Didier Deramond.

"He tried to sell (that) information but he didn't succeed," Deramond told CTV Montreal's Stephane Giroux.

The suspect is alleged to have approached a lawyer working for the Mafia and offered to sell the list, even divulging a few names on it to prove its authenticity, Giroux reported.

Deramond, a special investigator, said there is no indication right now that anyone is in danger, or that investigations have been compromised as a result.

"I can assure you right now that we contacted everybody and there is nobody in jeopardy," he added, noting that only two or three officers had access to the information.

Radio-Canada reported the unnamed former officer was asking for a six-figure sum in exchange for the list after retiring last January.

Deramond said police learned about the alleged offer to the Mafia through a wiretap investigation in April 2011. The retired officer suspected of trying to sell the list of informants was arrested in October, but no charges had been laid.

The case is in the hands of a prosecutor who will decide on any criminal charges.

Since the former officer had been with Montreal police for more than 30 years, Chief Marc Parent said the force was blindsided by the allegation.

"We are facing a person that decided not be honest and didn't respect the integrity of his job," Parent said.

While the chief noted that Montreal police have changed the way they handle sensitive data, one ex-biker and civilian undercover agent said that the damage has been done.

"Had it fallen into criminal hands there would have been carnage among informants and double agents," Eric Nadeau said.

The alleged leak also raises concerns among current informants about their safety in future investigations.

The current case isn't the only instance of similar charges.

Homicide detective Mario Lambert, who has been suspended from the force, is facing allegations he tried to sell confidential information to a known criminal. Plus, Angelo Cecere, an ex-RCMP civilian translator, will go on trial next month on charges he funneled information to the Mafia.

Other leaks are accidental: retired provincial investigator Guy Ouellette's laptop was stolen in one case. The computer contained sensitive information and was linked to the murder of at least one informant.