Oh, good.

According to Marylynne Pitz of the Pittsburgh Post-Gazette, in that city, 314 items have been stolen from the Carnegie Library’s rare books room. Making it more difficult to catch the thief is this fact: the theft was only discovered when an insurance appraisal was made in April 2017 … but who knows how long the materials had been missing by that point. The Oliver Room—the scene of the crime—has been closed since last April.

With no leads in the case, the authorities are looking for other antique booksellers to help them out. As Pitz reports:

At the urging of Detective Lyle Graber from the Allegheny County DA’s office, the Antiquarian Booksellers Association of America alerted its 450 members … The New York City–based organization’s email, dated March 6, included a spreadsheet listing the stolen items with titles, authors, publishers, publication date and a brief description of each work, but not in every case.

Susan Benne, executive director of the Antiquarian Booksellers Association of America, says that Graber contacted her in February and asked her to distribute the list.

Appraisers put the value of the stolen items at $5 million, possibly more. The pilfered volumes include a first edition of Isaac Newton’s Philosophiæ Naturalis Principia Mathematica dated 1687, from London. (In 2016, a copy of this book sold at auction at Christie’s for $3.7 million.) Also taken: a first edition of Adam Smith’s The Wealth of Nations, worth $150,000; a first folio of Edmund Spenser’s The Faerie Queene from 1609; and nine books printed before 1500 — within fifty years of Johannes Gutenberg’s first use of the printing press.

Library spokesperson Suzanne Thinnes says that the theft occurred “over an extended period of time,” and, ominously, appears to be the work of someone with close knowledge of the collection. This makes sense: the Oliver Room’s contents are rare and accessible only by appointment, as Julissa Treviño reports in Smithsonian, with several items held under lock and key. Thinnes also told media outlets that the staff member who oversaw the collection is no longer employed by the library, but the article doesn’t say whether that employee is a suspect.

According to Michael Vinson, a rare-book dealer contacted by the Post-Gazette, the fact that the stolen works cover such a wide swath of topics points to the crime being perpetrated by someone intimately knowledgeable of both the collection and the importance of the works it held:

“The books were immensely valuable. But they were also across a wide variety of fields. Only a few people have that knowledge … It has inside written all over it.”