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Between We Own the Night and the upcoming American Gangster, late-20th-century wars between New York area cops and drug lords are enjoying a new cinematic vogue. One of American Gangster’s supporting characters, Harlem heroin potentate Leroy “Nicky” Barnes, was doing very well for himself, his friends, his wife, and his mistress when a 1977 New York Times Magazine cover story dubbed him “Mr. Untouchable.” Jimmy Carter, spurred by the article, wanted the superdealer busted, and less than a year later, Barnes was convicted of drug trafficking and sentenced to life without parole. Yet that’s not where the story ends.

Director Marc Levin, whose previous film, 2005’s Protocols of Zion, was a first-person exploration of the latest rage for the scurrilous anti-Semitic text, takes a more detached approach to Barnes. Copping its title from the Times, Mr. Untouchable features the expected mix of archival footage, talking-head interviews, and ’70s soul standards—“Pusherman,” “Mr. Big Stuff”—to evoke the simultaneously clandestine and flamboyant world of a major “powder” dealer. Levin’s portrait is typical of the secondhand-documentary genre, even with the addition of quotations from some of Barnes’ favorite authors, Melville and Machiavelli. The opening titles say that Barnes “disappeared in 1986,” but he didn’t pull a Jimmy Hoffa. He testified against his former associates and—with the help of then U.S. Attorney Rudolph Giuliani—vanished into the witness protection program, from whose shadows he speaks to Levin’s camera.

Barnes’ silhouetted presence makes Mr. Untouchable more than just another after-the-fact doc. The one-time gangster has rejected the Mafia-style code of silence that once served him well in favor of Machiavelli’s every-villain-for-himself doctrine, and he’s as proud to be a successful snitch as he was to be a top dealer. (He brags that his testimony resulted in more than 75 convictions.) Levin flatters his subject by filming him in a boardroom, where he can preside over an empty conference table like a CEO who just fired all his VP’s. But if Barnes got his revenge, he doesn’t seem to have gotten much wisdom. It’s remarkable to spend some time with the former Mr. Untouchable, but he’s not all that interesting.