It is perhaps the most significant artifact documenting the arrival of Jews in the New World: a small, tattered 16th-century manuscript written in an almost microscopic hand by Luis de Carvajal the Younger, the man whose life and pain it chronicled.

Until 1932, the 180-page booklet by de Carvajal, a secret Jew who was burned at the stake by the Inquisition in Spain’s colony of Mexico, resided in that country’s National Archives.

Then it vanished. The theft transformed the manuscript into an object of obsession, a kind of Maltese Falcon, for a coterie of Inquisition scholars and rare-book collectors. Almost nothing was heard about the document for more than 80 years — until it showed up 13 months ago at a London auction house. The manuscript was on sale for $1,500, because the house had little sense of its value.

But last year the relic caught the eye of a prominent collector of Judaica, Leonard Milberg, when it showed up for resale at the Swann Galleries in Manhattan. It was now priced at more than 50 times what it had sold for just a few months earlier in England. Mr. Milberg consulted a variety of experts, who told him it might be the actual manuscript, and worth as much as $500,000. They also warned him to be careful — the original had been reported stolen.