Twenty-five years after the fall of the Berlin Wall, documentary filmmaker Petra Epperlein had painful personal reasons to return from the United States, where she now lives, to her hometown of Chemnitz in what was once East Germany. The city had been renamed Karl Marx City under the German Democratic Republic, a Soviet satellite from just after World War II. A decade after the Wall came down in 1989, Epperlein's beloved father destroyed all his papers and hung himself from a tree in the family's garden, leaving Epperlein and her twin brothers with lingering suspicions that their father may have been an agent of the GDR's notorious Stasi secret service.

He would hardly have been alone. The fascinating Karl Marx City, which Epperlein made with her husband Michael Tucker, is as much an inquiry into the mechanics of how autocratic regimes work as it is a search for the truth about one citizen's tragic end in its clutches. As one witness observes drily, if three people were seated together anywhere in the GDR, it was assumed that at least one of them was among the thousands of civilian informants dragooned or blackmailed into service to maintain round-the-clock surveillance for the Stasi. Everyone was suspect, though of what crime mostly remained unclear.

As in every totalitarian regime the prisons were full, as is graphically illustrated in Broken (Kaputt): The Women's Prison of Hoheneck, the beautifully animated short film that plays with Karl Marx City. But "prophylactic surveillance" — often by means of cameras hidden in the cracks of public and private spaces as well as more overt snooping — was the government's most potent weapon, creating a corrosive, ubiquitous mistrust that guaranteed anticipatory conformity in the population at large.

As one historian of the GDR notes in the film, self-censoring obedience is the hallmark of the modern dictatorship. This quietly creeping autocracy may be why so many, like Epperlein's mother (a painfully ambivalent participant in the film), look back on their past as "not that terrible — we lived our small life." It may also be why the filmmaker counts herself among those who succumbed after the regime toppled to "Ostalgia," a glossing-over of life under GDR rule that, critics have claimed, infected retrospective films like 2003's Goodbye, Lenin (for some, a satire; for others an overfond look back at Soviet-sponsored Communism) and the ridiculously sentimental The Lives of Others, (2006), in which an afternoon spent listening to Mozart is all it takes to turn a hardened Stasi agent into a fanboy for democracy and freedom.

Some of Karl Marx City is a straight talking-heads documentary, and none the worse for it: The contextual background filled in by historians and a highly perceptive expert on the wave of suicides during and after the GDR is essential viewing. Epperlein visit to the Stasi archives in Berlin, where to this day staff painstakingly piece together documents hastily shredded by secret service officials after the Wall came down, is riveting, as is the agonized testimony of a childhood friend's relative who admits to having been a Stasi apparatchik who routinely invaded "suspects'" homes looking for dirt, or just to drive them crazy by rearranging the furniture.

In its efforts to be artful, Karl Marx City suffers now and then from the same breathy tendency to overdramatize already incendiary material that marred Epperlein and Tucker's 2005 Iraq doc Gunner Palace. Shot in alluring black-and-white, the film grows slightly histrionic when Epperlein goes walkabout around her former haunts, boom in hand and wearing an expression of unrelieved solemnity, or when she deploys a cloying little girl's voice recollecting her childhood experiences in the third person. She gives little space to the bitter humor and satire that flourished below stairs in all quarters of the Soviet Union.

That said, the story of Epperlein's family tragedy is enormously moving. Juxtaposing Chemnitz today (the city still sports a bust of Marx's head so enormous it couldn't be felled along with other monuments to an era many would rather forget) with declassified espionage footage from the GDR's shameful past, she reveals a ghost town with a secret history whose exposure sparks a radical revision in the way the filmmaker comprehends a childhood she had remembered as idyllic. Epperlein gets a definitive answer to the question of whether or not her father was a Stasi informant. The reasons for his suicide remain opaque, but what becomes clear is that long after people have had enough and take to the streets and topple their oppressors, autocracies leave an appalling trail of collateral damage nursed in secret until, for their victims at least, it's too late.

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