Each February, Gilbert Michlin invites fellow survivors and their spouses to his birthday party at his home in Paris. Before making a l'chaim, Mr Michlin remembers how, two days before his 18th birthday in 1944, he was deported from Paris and sent to a slave-labour sub-camp of Auschwitz.

This year, Mr Michlin turned 85. For decades, he has been asking: why did Siemens keep him and 87 other slave labourers alive? What happened to the other men who worked for Siemens, in the heart of the Nazi killing machine?

Answers might be in the company archive. Its director, Frank Wittendorfer, says Siemens central archive in Munich has 2.5 linear miles of files, 400,000 photos and 3,000 films.

Secrecy surrounds the archives, most of which were moved from Berlin to Munich before the end of the war, to escape Allied bombings. It has been about as hard to get into these archives as into those in the Vatican.

For years, historian Wilfried Feldenkirchen oversaw the central archive - but in June 2010 he died in a crash of an electric model of a Siemens car.

Secrecy surrounds the files, which were moved to Munich

But now there are signs that Mr Michlin may get some answers. This month, the Siemens archive is to provide its files on Nazi-era operations at the Ravensbrück women's concentration camp to a major exhibition.

This could mean there is hope for Mr Michlin, who five years ago attended a historic, private meeting between Bobrek survivors and Siemens management and labour.

Now Dr Wittendorfer has said he plans improve access to the archives. Legitimate written requests will be honoured, but only those files that have been catalogued may be viewed.And slowly, Dr Wittendorfer and his staff are cataloguing miles of files so they will be searchable electronically.