Lynch presses FBI on source

The congressman, who participated in the hearings that led to widespread overhauls in FBI guidelines, said the briefing will help him gauge whether the FBI appropriately kept a relationship with reputed New England Mafia capo Mark Rossetti.

Rossetti is a suspect in six murders, law enforcement officials have told the Globe. He has been convicted of gun crimes and of robbing an armored vehicle, and last year he was charged by the State Police with running a sprawling criminal racket that included violence, extortion, and drug trafficking.

“I have some serious questions as to whether or not those guidelines were followed,’’ Lynch said. “It appears Rossetti was involved in some type [of way] in overseeing a rather widespread criminal enterprise, and so that should have become apparent to his handlers many months ago if he was being closely monitored.’’

Lynch added, “The timeline is very important here and also what was disclosed in terms of the activities of Mr. Rossetti and his associates. I’d like to drill down on that, hopefully in a way that doesn’t compromise the investigation but certainly gives guarantees to Congress that the guidelines are being followed.’’

The use of informants by law enforcement agencies has been allowed as a seedy but necessary tool in law enforcement, but the FBI has set up strict guidelines, particularly since the Bulger scandal. Among them, a handler is supposed to notify supervisors whenever an informant engages in violent crime, and that informant could be turned over to authorities for prosecution.

But the disclosure that Rossetti, reputedly a high-ranking Mafioso, was working with the FBI at the same that he was being targeted by the State Police raises questions about how closely the FBI was monitoring him, for how long, whether he provided useful information, and whether the bureau was aware of the extent of his alleged activities.