Hohenschoenhausen Prison in Berlin is the sinister reminder that even now, on the 20th anniversary this Sunday, the work to reunify Germany is still unfinished.

The complex of drab buildings was the secret detention jail for East Germany’s Ministry of State Security—Stasi—the vast and brutal internal army used to control the population. And Hohenschoenhausen, left untouched since Stasi agents fled when the wall came down, was the center of interrogation and torture.

“This was my cell,” said Vera Lengsfeld, who spent a month there awaiting trial as Stasi agents tried to force a confession to opposing the state. She did not know then that the man who betrayed her was her husband.

In the 1980s Vera Lengsfeld was a modest civil-rights activist in the Communist state, with three children and, friends say, very much in love with her husband, a poet. Today she is a trim 58-year-old with a blond bob who has become an influential member of the German Parliament, often at odds with Chancellor Angela Merkel (also a former East German) over individual liberty. She is no longer married.

Walking in what is now a museum, under harsh fluorescent light on long-faded brown linoleum, Lengsfeld stops outside another door. “This was where they did the water torture that made you think you were drowning,” she says without emotion. “And the one next to it was for the Chinese water torture.”

“Doesn’t being a guide here revive bitter memories?” I ask. “No, it doesn’t,” she says. “I give the tours to teach the truth about East Germany, especially to the young.”

In East Germany, there was nowhere Stasi agents or their informers weren’t watching or listening and reporting back to headquarters. Homes were bugged, telephones tapped, mail opened, neighbors spied on neighbors. According to German federal records, there were almost 100,000 Stasi agents and an estimated 500,000 informers under contract to the ministry in a country of 16 million people. Some informed to curry favor with the regime and others were induced with threats.

In Hitler’s Germany, there was one Gestapo agent for every 2,000 citizens. In East Germany, there was one Stasi agent or informer for every 63 citizens, records show.

Lengsfeld was under constant surveillance and harassment. She was expelled from the science academy where she worked and then made her living as a beekeeper and translator.

Finally, in 1988, she was arrested for carrying a sign in a government parade. It quoted the first line of the East German constitution: “Every citizen has the right to express his opinion freely and openly.” The charge was riotous behavior. She remembers that on her arrival at Hohenschoenhausen. “I was fingerprinted and then had to sit on a piece of fabric. That was then placed in a jar to collect my smell.” (Thousands of such jars were found after the wall came down but there has never been an explanation of forensic value, bizarre or otherwise.)

Convicted by a Communist court she was later thrown out of the country, leaving her husband, and her three children behind.

But the worst for Vera Lengsfeld was yet to come.

Tens of thousands of Stasi victims, whose lives were destroyed; who were beaten, tortured, kidnapped or killed, have never seen anyone who was responsible punished.

Thomas Habicht, a leading German journalist who was a target of Stasi agents in West Berlin, says that still casts a shadow over reunification. “The generation of Stasi criminals is still alive, behaves aggressively, and in some cases even has gained influential positions again.” Many of the former agents and officials, Habicht says, still live in the privileged housing built for them by the East German government “which adds insult to serious injury.”

On this subject, Lengfeld’s eyes flash for the first time this day. “I’m angry,” she snaps. While the first and only freely elected East German parliament moved to punish the Stasi agents, she and others believe that to speed reunification, the West German government of Helmut Kohl swept the issue under the rug and subsequent governments have kept it there. “Just look at pensions,” she says. “Because (the Stasi agents’) wages were two or three times higher than the average East German, their pensions now are two or three times higher” than most of the retirees. “East Germany,” she says, “had both victims and perpetrators and we cannot forget that.”

In November, 1989, as chaotic protests against the repressive regime grew, Lengsfeld wanted to return from her exile in Britain to be with her family. On November 9 she arrived in West Berlin and through confusion at the Friedrichstrasse checkpoint, she was able to slip back into East Berlin. Her timing was exquisite: that night the Berlin Wall fell.

The Stasi learned from her husband not only about her opposition to the government but intimate details of dinner table conversations, pillow talk, even their sex life.

In the aftermath, six million files on East German citizens were discovered in Stasi archives. Laid end to end they would be 125 miles long. In 1991, the files were opened for the Stasi victims. It was then that Vera Lengsfeld learned that that the Stasi informer code named “Donald” was her husband, Knud Wollenberger.

In 1984, Wollenberger signed a Stasi contract agreeing to inform on Lengsfeld and her son from a previous marriage. The Stasi learned from her husband not only about her opposition to the government but intimate details of dinner table conversations, pillow talk, even their sex life. She divorced “Donald” in 1992.

Today, she says, “I will never again talk about this.” But those who saw her then described a shattered woman, someone who felt violated in a way she could not at first fully comprehend like, say adultery.

Wollenberger, who suffers from advanced Parkinson’s disease, does not give interviews. But a decade ago when a television interviewer asked why he agreed to spy on his wife he said, “I didn’t think you could say no.” Was he forced to do it? “No.” Well, asked the interviewer, was it voluntary? Wollenberger answered with a question. “What is voluntary?”

There are certain echoes to this story in The Lives of Others, the Oscar winning movie about the Stasi and its victims. In the film—the only serious one on the subject—a playwright’s lover is induced to spy on him with tragic consequences. The playwright has long made his accommodation with the regime, but then turns against it.

Sebastian Koch, who portrayed the playwright, believes many in Germany, like his character, find the Stasi excesses too easy to ignore. “He refused to see it because things were too perfect and he was too productive,” Koch says, “but it will always be there, underneath the surface.”

At the end of the film Koch’s character meets the former minister of state security, still smug and arrogant. “And to think,” the playwright says, “that people like you once ruled a country.”

Habicht, the journalist, says, so far, that question has not been fully answered. “We still have thousands of Stasi victims who, 20 years after reunification, want to learn the truth from their files.”

According to Germany’s Federal Commission, which manages the Stasi archives, two and a half million people have read their personal files. Another six thousand are applying each month to gain access to theirs. Many former East Germans still do not know who spied on them, what was reported and the consequences.

At the same time, Sebastian Koch says Germans should never forget people like Vera Lengsfeld. “There is a larger truth here. You have to commit yourself and face the consequences. You have this moment when you have to react or surrender.”

Bob Jamieson has worked as a correspondent for NBC News and ABC News, reporting from all seven continents during his 40-year career. He has received five national Emmys as well as DuPont and Peabody awards.