Juergen Falter has devoted much of his academic life to studying Adolf Hitler's rise and Nazi Party membership records.
He believed he understood both the history and his own family's past.
Then he searched for his mother's name in newly digitised NSDAP files and found that she had been registered as a member since 1940.
He describes her as a liberal Catholic. The discovery shocked even a researcher who had spent decades in archives.
She had been classified as exonerated during post-war denazification and had never discussed possible party membership with her family.
Falter told CNN that, had his father — an anti-Nazi imprisoned by the Gestapo — known, he probably would not have married her.
Archives become widely searchable
His experience is not isolated.
German media organisations, including Die Zeit and Der Spiegel, have developed search engines allowing people to check whether ancestors belonged to the Nazi Party.
Historians already knew the records, whose physical membership cards are held in Germany's Federal Archives.
Previously, access required an application, time and sustained research.
The major change came when the US National Archives put microfilm of surviving membership records online.
Using artificial intelligence, German media processed information from more than twelve million cards into accessible databases.
Public interest was enormous.
Historian Katja Hoyer wrote in the Financial Times that the US archives website crashed under the traffic. More than 1.5 million people had accessed the digitised records by late April.
Die Zeit reported millions of visits.
The gap between national and family memory
The new access touches a sensitive issue: the distance between Germany's national history and individual families' stories.
After the war, millions of families preferred silence.
Schools and museums developed a substantial culture of remembrance concerning the Holocaust and Nazi crimes, while accounts inside homes were often less clear.
Grandparents were described as uninvolved, as victims, as soldiers who did not know, or simply as people trying to survive.
Former Green minister Renate Kuenast quickly searched for her father.
She found he had joined the NSDAP in 1933, the year Hitler became Chancellor.
“It was not a shock, but it hit me,” she wrote.
He died in 1995 without sharing that history.
A membership card is not a complete life story
Historians warn that the records do not provide all the answers.
The date of joining can offer clues. Before 1933, membership often indicated ideological commitment. After Hitler took power, some joined out of fear, self-interest or social pressure.
A card alone, however, proves neither the extent of someone's guilt nor their innocence.
A non-member could have participated in crimes. A member could have had a complex, even tragic, personal history.
Hoyer makes a similar point: the records raise more questions than they answer, but renewed questioning is itself important.
A politically charged moment
The new confrontation with the past comes as the far-right Alternative for Germany has long pressed the country to move away from what it calls a culture of guilt and focus more on national pride.
The AfD finished second in the previous year's national election, reinforcing concerns that remembrance of Nazism was losing its deterrent power.
Searching the archives therefore has a broader significance than discovering whether a grandparent possessed a party card.
It raises questions about how ordinary people can turn towards radicalism during periods of crisis, fear and social pressure.
As the generation that lived through Nazism passes away, memory increasingly moves from family accounts to documents, archives and historical research.
The challenge is not simply to remember what happened, but to ask again how it happened.
