Vivian Maier worked as a housekeeper and governess in Chicago while keeping a hobby of street photography. (Vivian Maier/courtesy of the Maloof Collection)

How odd that the documentary “Finding Vivian Maier” should arrive in theaters alongside “Hateship Loveship,” a fictional drama starring Kristen Wiig. In the latter film, Wiig stars as a quiet, enigmatic housekeeper and nanny who nurtures an improbably rich inner life, which she commits to creating the reality she’s silently yearned for. “Finding Vivian Maier” tells something of the same story, about a fascinating real-life artist who has only come into her own years after her death.

In 2007, John Maloof, a young writer working on a history of the Chicago neighborhood where he grew up, purchased a cache of photographic negatives at auction that he quickly surmised wouldn’t be of much help in his research. He set them aside, only later examining them further to conclude that they were, in fact, brilliant examples of mid-20th century street photography. They were made by Vivian Maier, a Chicago woman with no dis­cern­ible footprint in the art world or digital universe at large. Intrigued, Maloof began to acquire more of her negatives, as well as boxes of undeveloped rolls of film. Using the scores of receipts, notes, scraps of paper and detritus Maier had hoarded throughout her lifetime, Maloof managed to get in touch with the people who had known and worked with her from the 1960s until her death in 2009.

Together with Charlie Siskel, Maloof has made a chronicle of his investigation with “Finding Vivian Maier,” in which he discovers that his subject worked as a housekeeper and governess in Chicago’s prosperous North Shore neighborhoods (including, for a brief time, for television personality Phil Donahue). Interviewing the parents and grown-up children she worked for, then widening his detective story to ferret out Maier’s roots in France and New York City, Maloof creates an absorbing, often disturbing portrait of a woman who used her tremendous height (around six feet) and imposing personality to create an almost impenetrable carapace around herself. That stance also allowed her to deploy her Rolleiflex camera to photograph people undetected or, if they saw her, with brazen disregard of their privacy.

The results of her amateur pastime were stunning. When Maloof shows her images to the photographer Mary Ellen Mark, she compares Maier’s work to that of Helen Levitt, Robert Frank, Lisette Model and Diane Arbus. Joel Meyerowitz, himself a master of spontaneous, from-the-hip street portraits, pronounces Maier’s work as suffused with the kind of human understanding, warmth and playfulness that proves she was “a real shooter.”

That doesn’t necessarily mean she was a straight shooter. Known by various names throughout her working life, Maier maintained a fierce aura of mystery, and although she was clearly sympathetic to the vulnerabilities and lonely emotions of childhood, she was capable of shocking cruelty, as one of her former charges recalls. One of the great strengths of “Finding Vivian Maier” is the filmmakers’ willingness to gently thread ethical inquiry in and out of the film, whether those questions have to do with class (few of the privileged kids Maier took care of ever thought to ask her about her life) or her own behavior with them and the people she photographed.

Many of those subjects were poor, sometimes in an addled or inebriated state; in some cases it’s clear that they’ve consented to Maier’s ministrations but in others, that implicit contract is barely acknowledged, let alone respected. Then again, the photographer herself didn’t print her pictures — it’s Maloof who, quite possibly in abrogation of Maier’s own wishes, is making her work known today. “Finding Vivian Maier” addresses all of these thorny questions with admirable honesty, all the while treating viewers to the exquisite photographs that possess undeniable power, poetry and haunting melancholy. They’re the best part of a film that leaves a large part of its subject’s mystery gratifyingly intact.

★ ★ ★

Unrated. At Landmark’s E Street Cinema. Contains brief disturbing images. 83 minutes.