The Oliver Room in the Carnegie Library of Pittsburgh is home to books, atlases and other items so rare that it’s off limits to the public. Only scholars and researchers can visit by appointment.

But that didn't stop someone (or someones) from stealing 314 books and items from the room, as the museum discovered last spring during an insurance appraisal. The case is currently under investigation, and a full list of stolen items has been published on the Pittsburgh Post-Gazette.

While the library did not provide the exact value of the items, rare books dealer Michael Vinson tells the Post-Gazette's Marylynne Pitz that the missing items were "easily worth" $5 million. “This is an immense cultural crime,” he adds.

Among the stolen objects are nine books printed before 1500; and a 1687 first edition of Isaac Newton’s “Philosophiae Naturalis Principia Mathematica.” A first edition of Adam Smith’s “The Wealth of Nations” was also taken.

Located on the third floor of the main branch of the Carnegie Library system in Pittsburgh’s Oakland neighborhood, the Oliver Room was always under camera surveillance, as WPXI reports, and only a few library employees had access to the room. Since April 2017, it has been declared a crime scene and it has remained closed as detectives from the Allegheny County District Attorney’s Office investigate the case.

In a statement to media outlets, library spokesperson Suzanne Thinnes says the items were likely stolen over an extended period of time by someone familiar with the Oliver Room and the library.

“This is a great loss to the Pittsburgh community,” she says. “Trust is a very important component of what we do on a daily basis… Our goal is to recover those stolen items.”

Since the items would likely only be valuable to collectors, investigators asked the Antiquarian Booksellers Association of America to alert and release a list of the stolen items to its 450 members in the hopes that it will lead to their recovery.

Library theft became a criminal offense in the state of Pennsylvania with the Archives, Library, and Museum Protection Act of 1982. As Megan Cottrell reported for American Libraries magazine in 2015, many library thefts are inside jobs, committed by library staff members who have knowledge of and access to valuable rare books and items.