For more than 60 years Elfriede Lina Rinkel hid a terrible secret. To her family, friends and Jewish husband Fred, Mrs Rinkel was one of many Germans who had fled to the US after the second world war seeking a better life.

But yesterday the 84-year-old's extraordinary past caught up with her. American officials said Mrs Rinkel had been deported from her San Francisco home to Germany after US investigators discovered she had worked as a guard in a Nazi concentration camp.

Mrs Rinkel's shocked relatives, who did not want to be identified, said yesterday they had had no idea about her wartime activities. She had concealed her past for half a century not only from them but also from her husband - a German Jew who fled the Holocaust. He died two years ago and almost certainly knew nothing of the truth, they said.

"It knocked us off our feet," Mrs Rinkel's sister-in-law told the Oakland Tribune newspaper. "We have many Jewish friends who live in the Oakland/Berkeley area. This would be quite shocking for them as it was to us."

According to the US justice ministry, Mrs Rinkel worked at Ravensbrück concentration camp, north of Berlin, from June 1944 to April 1945. She used an SS-trained dog. Documents released by the ministry's office of special investigations, set up to track down fugitive Nazis, include her service card, taken from an SS centre, and bank records.

The camp, completed in 1939 by the SS leader, Heinrich Himmler, was built almost exclusively for female prisoners. Within a few years it had evolved into a brutal slave labour camp where "undesirable" women - first German opponents of the Nazi regime and prostitutes and criminals, later Jews and Gypsies - were held, experimented on and killed.

More than 130,000 women passed through Ravensbrück, near the town of Fürstenberg. Most came from Poland or the occupied Soviet Union. Only 40,000 survived. The Red Army liberated the camp in April 1945, but arrived after Nazi troops took thousands of inmates on a forced march, where many died.

Last night Ephraim Zuroff, the head of the Nazi-hunting Simon Wiesenthal Centre in Jerusalem, said Mrs Rinkel's story was typical. Many low-ranking Germans who collaborated with the Nazis kept silent about their role to family and friends for decades afterwards, he said. He conceded, however, that what made Mrs Rinkel's case extraordinary was that she had then married a German Jew. "In my profession you often come across close family members who didn't have a clue what their parents, grandparents, uncles, aunts or sisters had done during world war two. The most painful moment is when they find out. The kids are always devastated.

"But I would never make the mistake of having any sympathy for these people. Ravensbrück was a concentration camp. Thousands of people died here as a result of Nazi policies."

Since Mrs Rinkel's return to Germany this month, her whereabouts is unknown. Yesterday officials from Germany's Nazi investigations unit told the Guardian they would not try to arrest her since any crimes she might have committed would have "expired". Under Germany's statute of limitations, only murder committed while working for the Nazis can be investigated.

According to her sister-in-law, who was married to Mrs Rinkel's brother, Fred Rinkel had no idea of his wife's dark past. His funeral service was held at a Jewish memorial chapel and he was an active member of the Jewish service organisation B'nai B'rith. "He had to leave Germany during all that terrible stuff that happened there and had to relocate in Shanghai," she said. "A lot of the Jewish Germans went to Shanghai."

According to US charges filed in April, Elfriede Huth was born July 14 1922 in the east German city of Leipzig. She applied for a US immigrant visa in Frankfurt in 1959. The application told her to list all her residences from 1938, but she omitted Ravensbrück. She was admitted to the US in September 1959 at San Francisco, the document says.

Her sister-in-law said Mrs Rinkel had met her husband decades ago at a German-American Club in San Francisco. She lived in the US until her deportation. "We did help her to close up her apartment and helped her to buy her airplane ticket and go to the airport and buy her luggage - but never a word about why she was leaving," she told the newspaper. "We thought she was going because her situation in her apartment had deteriorated."

Mrs Rinkel had arthritis, and her flat's lift was often out of service. "She said she just wanted to go back to Germany ... we believed her."

German historians said Mrs Rinkel had been one of about 3,500 young, unattached and mainly uneducated women from Germany and Austria who were overseers at the camp, some of whom were later executed. Horst Seferens of the Brandenburg foundation that now administers Ravensbrück said in the summer of 1944 hundreds of women had been forced into employment: "Many SS men had been sent to the front. The number of camps was rapidly expanded. More women were needed to watch over the growing numbers of prisoners."