Just as anonymous sources shop the information to the news organization that will give them the best ride, informants can shop their information to the best bidder—the local patrolman, the local sergeant, a detective, the state police, the DEA, the FBI, or the ATF.
What do both anonymous source and informant say to journalist and cop after they've spilled important beans? "You've got to protect me on this." Whether they like it or not, journalists and cops become invested in their sources and informants, and as the relationship ages, the investment turns into dependence. I don't know if Connolly started off crooked or if he pimped himself out in increments until there was no moral daylight between him and Bulger. I doubt that many reporters commence their source relationships thinking that politicians may eventually own them—or even sense it when they become the pol's property. I so hate it when reporters refer to "My candidate" or to "my sources." Don't they know who is property and who is the real owner?
These relationships—like your relationship with your plumber or your auto mechanic—are fraught with deception and double-dealing. If you dispense information for favors or protection, you must always keep a stash hidden, because the time will come when you'll need it to buy your way out of a jam or to purchase a favor. In other words, neither a source nor an informant has an incentive to tell all, but both have every incentive to dribble out information slowly and incompletely to keep the recipient captive.
But, of course, it's a two-sided game. Journalists and cops can always rattle their sources and informants by implying that they know more than they do. They can also blackmail their sources and informants by saying that they're going to write a story or file for an arrest warrant based on what they know—and then wait for the reaction. If properly played, the gambit will force sources and informants to sing like Ethel Merman.
I'm not saying that no anonymous source and no police informant can be trusted or that all dealings with sources and informants are inherently corrupt—just that all information-trading relationships can be easily corrupted. Have you looked at your marriage lately?
Don't you dare look at my marriage. Send your most valuable secrets to me via email: email@example.com or watch me lip-synch Cole Porter tunes on my Twitter feed. (Email may be quoted by name in "The Fray," Slate's readers' forum; in a future article; or elsewhere unless the writer stipulates otherwise. Permanent disclosure: Slate is owned by the Washington Post Co.)