Sometimes a documentarian can only be as good as the material available, and that turns out to be a severe limitation for directors Alon and Shaul Schwarz in the telling of “Aida’s Secrets.”

Izak Szewelwicz was born in 1945, just after the end of World War II, in the Bergen-Belsen displaced-persons camp, set up by the Allied forces near the Nazi concentration camp of the same name. Izak was sent to Palestine for adoption as a toddler and grew up (and still lives) in Israel, not learning until he was 10 that he was adopted.

Izak had a relationship with his birth mother, Aida, who lived in Canada. What he didn’t know, until he saw some records from Bergen-Belsen, was that Aida had another child — a younger brother Izak never knew he had.

The Schwarzes, aided by an investigator for a genealogy website, help Izak unravel the mystery. They find his brother, Shep, in Winnipeg, Manitoba — and Shep had no idea his mother lived a short flight away, in a nursing home in Quebec. Izak meets Shep, a blind former Paralympic athlete, and together they have a tearful reunion with Aida.

Mysteries remain, such as whether Izak and Shep had the same father. But Aida is stubbornly unwilling to divulge any information. “That’s in the past” is her mantra, and she refuses to budge.

The Schwarzes do uncover a few details and find another mystery that lands like a bombshell toward the movie’s ending. But they are hamstrung by the aged Aida, whose long-held privacy — or perhaps fear of embarrassment — denies the filmmakers the tidy ending they sought.

Even though “Aida’s Secrets” lacks a big, satisfying payoff, there are small joys along the way. The most exhilarating is the sheer joy Izak and Shep, men in their 70s whose toughest years were before their wisdom teeth came in, show in re-establishing their family ties.

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Aida’s Secrets

A tangled family tree and a mother’s reticence at reopening the past make for an intriguing but sometimes distant documentary.

Where • Broadway Centre Cinemas.

When • Opens Friday, Dec. 8.

Rated • Not rated, but probably PG-13 for language and mature themes.

Running time • 95 minutes; in English, and in Hebrew with subtitles.