Benoît Roberge was a top Montreal police investigator known for his grasp of Quebec's criminal bikers. He handled key police informants, testified as an expert witness at trials and worked hand-in-hand with police specialists on battling organized crime.

Now Mr. Roberge stands accused of helping the very criminals he was assigned to investigate. In an arrest that has shaken police ranks and had reverberations as far as Quebec's criminal prosecutions office, Mr. Roberge was picked up by his own on Saturday and faces charges related to selling sensitive police information to criminal bikers.

Mr. Roberge, 50, was led into court in handcuffs Monday and stood in a prisoner's dock to be arraigned on charges of obstructing justice, breach of trust and participating in the activities of a criminal organization.

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"This situation is taken very seriously," Inspector Michel Forget of the Sûreté du Québec said earlier in the day. "All resources available were put in place to shine light on the circumstances surrounding this leak of information to organized crime."

Police began to probe Mr. Roberge, who retired this year with a reputation as one of the province's most experienced biker specialists, after they became worried that details of sensitive probes were being leaked. They quietly began an internal investigation that lasted for months.

According to Radio-Canada, Mr. Roberge was funnelling information to René Charlebois, a Hells Angels hit man and high-ranking biker who was serving a life sentence for murder until he escaped from prison three weeks ago. He was found dead 12 days later, just as the police were closing in on him. The broadcaster said police began probing Mr. Roberge after the biker's death.

Mr. Roberge went to work in March as head of the intelligence unit at Revenu Québec. In a statement, the tax agency said it had suspended Mr. Roberge and was co-operating with the police investigation.

The impact of Mr. Roberge's arrest even reaches into the domain of criminal prosecutions. Mr. Roberge's wife is a Crown prosecutor in Montreal assigned to an office probing organized crime. No decision has been made about her caseload, a spokesman for the prosecutors' office said.

According to Mr. Roberge's indictment, his alleged offences took place in St-Denis-de-Brompton, near Sherbrooke, starting in January, 2010, when he was still employed with the Montreal police, and continuing up to this month.

During his career, Mr. Roberge had made a name for himself in the highly specialized world of criminal bikers. He was a former controller of the late Dany Kane, a biker who worked undercover for the police and played a key role in the crackdown against the Quebec Hells Angels in 2001. Mr. Kane was a member of the Rockers, the puppet gang of the Hells Angels' Nomads, the top chapter that spearheaded the murderous biker turf war of the 1990s. After initially working for the RCMP, Mr. Kane was eventually handled by Mr. Roberge and an SQ colleague, Robert Pigeon. They talked to him by phone daily, debriefed him in person, got him to wear a body pack and recorded his video statements. He tipped them about upcoming biker meetings, which police secretly recorded.

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Mr. Roberge also often showed up at biker gatherings, checking who visited their clubhouses. He testified as an expert witness in a major case against the Rock Machine, in the mega-trials against the Quebec Hells Angels and in the landmark Ontario case against the Hells Angels' Steven (Tiger) Lindsay and Raymond Bonner, which ended with the club being deemed a national criminal organization.

The allegations against Mr. Roberge came two years after another retired Montreal police detective, Ian Davidson, killed himself as he was being investigated for trying to sell the names of secret police informants to the Mafia. The investigation leading to Mr. Roberge's arrest included the Montreal police, provincial police, RCMP and the Quebec revenue agency.