Because he’s not telling, no one knows whether the answer to the question that vexed author Chanan Tigay for five years is now in plain sight at the Sutro Library at San Francisco State University (see related story).

The key that unlocked the mystery may be part of a current exhibit titled “Treasures from the Yemenite Hebraica Collection,” consisting of 22 Yemenite Hebrew scrolls and manuscripts dating from the 13th to 19th century.

And it may not.

“Chanan won’t say yet because the book won’t be out until April 12,” said Diana Kohnke, the archival librarian who curated the exhibit. “Until I am able to read the book, I won’t know exactly what he found here.”

Tigay’s research into whether the Book of Deuteronomy “discovered” by Moses Wilhelm Shapira in the 1880s was bogus or legitimate inspired Kohnke to put together the exhibit.

What she does know is that Tigay looked through all 167 Yemenite Hebrew manuscripts that Adolph Sutro, San Francisco mayor from 1895 to 1897, purchased in 1884 from Shapira’s estate.

When Tigay told Kohnke he was working on a book, she decided this spring would be the perfect time to exhibit some of the materials, along with other Yemenite Hebraica in the library’s collection.

“The Yemenite manuscripts haven’t been out of the boxes in years and, to my knowledge, they have never been exhibited,” Kohnke said. “These aren’t just fragments of scrolls and manuscripts. These are amazing artifacts, and they are important to Jewish history.”

The exhibit includes Sutro’s receipt from Shapira’s estate, which indicates the manuscript collection sold for 200 English pounds. That works out to about $36,000 today, Kohnke said.

In 1913, Sutro’s heirs donated his extensive collection of artifacts to the California State Library with the stipulation that the collection stay in San Francisco. The Sutro Library operated in various locations in the city for nearly 100 years, moving to its permanent home at SFSU in 2012.

The exhibit, displayed in three long glass cases and an upright glass cabinet, includes scrolls with talismans to ward off the evil eye or to promote fertility, Medieval books and bound manuscripts written on lambskin or calfskin (vellum). One of the scrolls is a 92-foot-long Hebrew Bible written on buff-colored leather with inserted pages penned on yellow leather.

A Torah scroll, dating from the late 1100s, is believed to bear Moses Maimonides’ “signature,” which means the philosopher and codifier may have written it. A scroll of the Book of Esther, made in Jerusalem in the 1880s, is in black ink on red vellum. Another eye-catching item is a book by Isaac Cardoso, published in 1679, that serves as the author’s defense of Judaism to Jewish people and also defends his choice to live as a Jew in Amsterdam.

Another book in the display was printed in 1546 in Venice. “This is interesting because in 1533, all Hebrew presses in Venice were closed by papal decree,” Kohnke said, “and at the time, Hebrew books were being burned all across Italy.”

A Mishneh Torah from 1383, with Oriental rabbinic characters, is displayed with an ornamental manuscript box crafted in a monastery in Jerusalem.

In his day, Shapira failed to convince the British Museum that some materials in his possession were authentic. All the items on display at the Sutro Library are.

“These are real,” Kohnke affirmed. “The collection purchased from Shapira’s estate has been catalogued four times, and none of the researchers or experts have doubted the authenticity of the scrolls.”

In his quest to build an extraordinary public research library, Sutro collected more than 250,000 manuscripts and rare books.

“He wanted to make San Francisco a world-class urban center and he wanted to put the best library in the world right here,” Kohnke said. More than half of his collection was destroyed in the fires triggered by the 1906 earthquake.

In addition to the Yemenite Hebraica scrolls and manuscripts, the Sutro Library also houses some William Shakespeare folios (rare collections of Shakespeare plays created in the 1600s), the letters and papers of British explorer and naturalist Joseph Banks, and materials on Mexican culture, religion and politics from 1540 to 1889.

“All these materials make history come alive,” Kohnke said, “and the Yemenite Hebraica collection includes a good mystery.”

“Treasures from the Yemenite Hebraica Collection,” through June at Sutro Library, J. Paul Leonard Library, fifth floor, 1630 Holloway Ave., S.F. Free. 10 a.m. to 5 p.m. Monday through Friday (closed April 14 and holidays).  www.tinyurl.com/sutro-library or (415) 469-6100