The ancient town of Nasielsk still sits just over 30 miles north of Warsaw, Poland, its population roughly the same that it’s been for over a hundred years — just over 7400.

But a huge number of its citizens were hauled away in just two days of December of 1939, when Germans and German sympathizers rounded up the thousands of Jews there and shipped them off, the vast majority of them transported to their doom.

In 2009, Glenn Kurtz stumbled across a cracked, shrunken and decaying roll of film that his grandfather David shot there and left behind in his home in Palm Beach Gardens, Florida. In the summer of 1938, he’d just bought the Kodak movie camera, and David and his wife Lena, who’d emigrated to the United States from Poland and prospered in Brooklyn, returned to Europe for a “Grand Tour” — Paris, Amsterdam, Zurich, Warsaw — and the towns Lena and David grew up in.

Just 13 months later, Nazi Germany and Soviet Russia invaded and dissected Poland, beginning World War II in Europe. Warsaw and everywhere else Lena and David visited in Poland was forever changed, or in some cases, obliterated.

When grandson Glenn Kurtz started digging into the anonymous, unidentified vacation film, he eventually figured out where this three and a half minutes of footage was shot — his grandfather’s hometown, Nasielsk. Donating the film to the United States Holocaust Museum, where it was restored and posted online, Kurtz investigated and put out feelers, and slowly started piecing together some of what we see in those three and a half minutes or so — the trees, the Synagogue, a market, the Mezuzah boxes hanging next to each door in of the buildings in the square. After four years of digging and a few lucky tips, he wrote an acclaimed book about the lost world these grainy, faded images from the past preserved.

Dutch filmmaker Bianca Stigter uses that footage — and pretty much just that footage — for her fascinating forensic documentary about Kurtz’s research, “Three Minutes: A Lengthening.” Stigter parses the film as it unspools over and over again, a collection of often poorly-framed shots of streets, with lots of locals — many of them kids — smiling and crowding themselves into the frame. She pauses for freeze-frames and zooms in as Kurtz, never seen on camera, relates what he, the Holocaust Museum’s Steven Spielberg-backed preservationists and effects restoration specialists did to try and figure out what this store was, how that face could be rendered sharper.

A historian, a couple of survivors and children or grandchildren of survivors speak as the footage became known enough for word to get around and for faces to be identified. We hear about the button factory and the hierarchy of Jewish society there, symbolized by the sorts of caps boys from different classes wore.

And actress Helena Bonham Carter, in voice-over narration and performing the translated questions of the filmmaker, ponders the mystery, breaks down the chemistry of celluloid from that era and notes that reds still show up in the faded footage because “the color red fades the slowest.”

She muses about how unmoored we are when we can’t place where some piece of film is from, the context we reach for and the “absence” that footage like this preserves, doomed people with no idea of their fate, smiling in a place about to be forever changed, scarred by war and genocide.

Many faces remain unidentified, their families wiped-out, and the few survivors left are unable to recognize everyone. Apparently no attempt was made to find non-Jewish elders of the town to see if others could be identified. But as historical accounts of the mass deportation recited here make clear, Polish prejudice was at its ugliest during that December, 1939 roundup. And the town was further depopulated when a thousand non-Jewish Poles were deported a year later as Nasielsk became home to a German forced labor work camp.

There are also no clips of the town as it looks today, just images of a model of the square where these three minutes were filmed used to show “this is what it looked like.” That omission leaves the viewer as lost as Kurtz was when he first looked at what his grandfather had filmed and not labeled. We must wait for explanations, and watch and re-watch the footage for clues and context.

Like the even more impersonal documentary “From Where They Stood,” which investigates and recreates Holocaust photographs of sites now crumbled or overgrown, the impression “Three Minutes” leaves is that it’s more probing than moving, more of a mystery to be unraveled than an emotional journey into who and what were lost. It’s still quite worthwhile as history and as a meditation on tragedy and the nature of filmed memory.

Stigter has taken Kurtz’s research and his grandfather’s restored footage and turned those “Three Minutes” into something of a flickering filmed “In Memoriam,” letting us hear a bit about the Kurtzes, moments from history and anecdotes from life in Nasielsk and the people whose existence has been wiped from memory, save for this snippet of a family’s vacation film taken just before disaster struck.

Rating: PG (Holocaust anecdotes)

Cast: Glenn Kurtz, Maurice Chandler, and Helena Bonham Carter

Credits: Scripted and directed by Bianca Stigter, inspired by the book “Three Minutes in Poland: Discovering a Lost World in a 1938 Family Film.” A Neon release.

Running time: 1:12