JOSEPH GOEBBELS, in a pinstripe suit, his hair slicked back, gave a simple but philosophical speech about the importance of music. Then, smiling, he handed over the violin to a young woman.

The passing was captured on film: the violin’s elegant outline, the figure on its flamed-maple back, the wear pattern of its varnish.

Japan’s ambassador to Germany, Hiroshi Oshima, was on hand to witness the transfer. Nejiko Suwa, 23, played her new gift on the spot....