Of course my interest is heightened because the instrument in question may be a Stradivarius. But is it?

The expert searching for authenticity looks for subtleties of identity. The wood selection may reveal geographic information specific to the maker. The character and quality of the varnish, its method of application, and the ground that penetrates the wood underneath may be indicative of authorship. The connoisseur considers workmanship, style, and idiosyncrasies, including tool marks, techniques of construction and mastery, or the lack of it. The maker’s design and execution of the f-holes cut into the shell-thin belly, or the carved nautiluslike scroll are just some of the hallmarks of a maker’s hand.

And then there is the label.

Violin makers have been placing labels inside violins for hundreds of years, just as others have been tampering with them to increase their value by adding, say, a famous name. Two days after Goebbels gave Ms. Suwa the alleged Stradivarius, a Japanese newspaper said the violin dates from 1722, a year that resulted, by some estimates, in 20 violins from Stradivari.

In 1722 Stradivari would have been 78 years old. Although no one is certain, experts speculate that he made roughly 1,100 instruments before his death in 1737. Far fewer are extant.

When Ms. Suwa received the violin, she was already a violinist on the rise. Born in 1920, she was a prodigy by 10 and studying with the Russian violinist Anna Bubnova-Ono, Yoko Ono’s aunt by marriage. In 1936 she left Japan for Brussels and moved to Paris in 1938 to work with Boris Kamensky. She had her debut in Paris on May 19, 1939, just a year before the Nazi invasion of France.

Ms. Suwa performed throughout Europe during the war. She was a featured soloist with the Berlin Philharmonic in October 1943, and two months later Goebbels wrote his second and last diary entry about her:

“At noon I am a guest with Oshima. The famous Japanese violinist Nejiko Suwa plays for us a concert by Grieg and some smaller bravura pieces, with a superb technique and a brilliant display of art. I had given this violinist recently a Stradivarius violin as a present. By the way she plays I noticed that the instrument is in good hands with her.”