“Frank Serpico” is a finely etched and fascinating documentary. Directed by Antonino D’Ambrosio, it’s a portrait of the legendary Brooklyn-born Italian-American cop who blew the whistle on New York police corruption in the late ’60s and early ’70s — and, of course, it’s a movie you can hardly watch without comparing it to “Serpico,” the 1973 Sidney Lumet drama, starring Al Pacino in the title role, that became a classic of New Hollywood street grit and moral urgency.

How accurate was “Serpico”? The short answer is: very. It stuck close to the 1973 Peter Maas book, and “Frank Serpico” reveals just how much of Serpico’s story became, through the movie, iconic. As it turns out, the legend and the truth match up nicely.