An etching by Rembrandt worth between $20,000 and $30,000 and an engraving by Albrecht Dürer worth $600,000 are missing from the Boston Public Library’s print collection, according to the Boston Herald.

The Boston Public Library is working with the Boston police and the FBI in an investigation. Police Commissioner William B. Evans said that the art could have been missing for months before they were reported missing on April 29th.

Only a few people have access to the “secure, alarmed area of the Central Library in Copley Square where the treasured pieces were kept.” One of those people was Susan L. Glover, Keeper of Special Collections, who was placed on administrative leave on April 20th. It is unclear if she is a suspect in the case.

The Metropolitan Museum of Art holds a version of the missing “Self-Portrait with Plumed Cap and Lowered Sabre” by Rembrandt in its collection. The missing version came into the BPL collection as part of the Wiggin Collection in 1941.  Albert H. Wiggin was the president of Chase Bank of New York and collector of Old Master prints, early twentieth century French, British and American works of art on paper.

The other missing work, “Adam and Eve” (also known as “The Fall of Man”), was donated to the BPL in 1958 by Leo M. Friedman and is considered an “early masterpiece” in Dürer’s career. In the Boston Globe, Sebastian Smee writes that the 1504 engraving “combines [Dürer’s] astonishing ability to render detail in an intensely naturalistic way with a new type of idealized human beauty… The image itself is dense with symbolic details intended to impress and beguile a learned audience.” Those details—including a goat, parrot, a mouse and cat—are meant to show a peaceful scene before the Fall.

Boston Mayor Martin J. Walsh will meet with the board of the Boston Public Library this week to discuss the investigation and how to prevent such a loss in the future. Mayor Walsh told the Boston Globe:

“You can’t lose $600,000-plus of artwork in the city of Boston and have a good rationale for it,’’ Walsh said. “If there is an audit, it will be led by the mayor’s office, not by the library.’’