Boston police are investigating whether a Boston Public Library employee stole two art prints valued at more than $600,000 from the central branch in a theft that went undetected for as long as a year and raises concerns more artwork may be missing, authorities said Wednesday.
“We’re looking at the possibility of it being an inside job,” Boston Police Commissioner William B. Evans told reporters Wednesday, as authorities revealed that the FBI is assisting in the investigation.
One employee has been placed on paid administrative leave, said a library spokeswoman, who provided no further details.
Asked if any employees had been identified as suspects, Evans said: “I think we’re looking at some. . . . We’re looking at a few people inside who might have access to that particular area.”
The commissioner said he was informed that the prints may have been missing for up to a year.
One of the prints, an Adam and Eve engraving by Albrecht Dürer, is valued at over $600,000; the other, an etching of a Rembrandt self-portrait, is worth $20,000 to $30,000.
Evans said police were alerted a few weeks ago and immediately launched an investigation.
Library spokeswoman Melina Schuler told the Globe the library does not have images of the prints.
Mayor Martin J. Walsh said he was alarmed that the theft went undetected for so long and that library officials delayed notifying police.
He said it was also troubling that the library does not have images of the missing prints.
“We can’t have valuable treasures of the city of Boston disappearing,” Walsh said during a brief telephone interview Wednesday. “We need to catalog what we have and make sure we are keeping an eye on them. Prints can’t just walk out the door.”
Walsh called for a review of library security and said he would meet next week with the chairman of the library’s board of trustees and the library’s president, who is on a trip outside the country.
The mayor said he was unaware of other missing items.
“But certainly I have concerns,” he said.
The library president, Amy Ryan, said in a statement Wednesday that the library in Copley Square is working closely with police on the investigation and conducting an independent security review and an item-by-item audit of its print collection, which has more than 200,000 pieces.
“It is important that all of the treasures of our collection can be made available to the public now and in the future, and that must be balanced with ensuring their security,” Ryan said.
Schuler, the library spokeswoman, offered more details about the sequence of events. She said that when library workers discovered the Dürer missing April 8, they launched a search in locations where the print may have been misfiled.
On April 15, the staff discovered the Rembrandt self-portrait also was missing and notified the police commissioner and the mayor, she said. A police report was filed April 29, and the Boston Police Anti-Corruption Unit launched an investigation.
Jeffrey B. Rudman, chairman of the library’s board of trustees, said in a statement that the trustees have “endless confidence in President Ryan.”
Rudman said that Ryan notified police “when she first knew exactly what artwork was missing,” and that the trustees appreciated the efforts of Ryan and her staff “both in their cooperation with the police and in doing all that they can to maximize the likelihood that we will recover this art.”
Recently, the library enlisted an independent security firm, KCMS Safety and Security Solutions, to work with its staff to assess security systems in the print department and associated collections and to make recommendations for upgrades, Schuler said.
The artwork was stored in a print room that is closed to the public. Patrons who want to view items must complete a card with personal information.
Then, a staff member — roughly 10 to 20 people on staff are authorized to do this — retrieves the items from the print room, which is accessible only via staff elevators.
Patrons view the items in a reading room, which is locked and tucked in the rear of the rare books section, past glass cases that hold ancient books. They are not allowed to bring bags into the room, and they are monitored by a librarian.
Paul Crenshaw, an associate professor and chair of Providence College’s art history department, said Dürer, a 16th-century German artist, was the first major artist who dedicated himself to print making. The “Adam and Eve’’ print, he said, is among the best-known of his works.
The Rembrandt self-portrait is one of many done by the artist and far less valuable.
As for why someone chose those two prints from the library’s collection, which includes 30 Rembrandts and 105 by Dürer, Crenshaw said, “It probably tells you that someone knew what they were looking for and took something particular that they wanted.”
Anthony Amore, director of security at the Isabella Stewart Gardner Museum and author of two books on art thefts, said: “Thefts happen at libraries all the time. Most people are unaware that many public libraries have exceptional art collections.”
The Gardner Museum was the site of the biggest art heist in history. The 1990 theft remains under investigation by the FBI, the US attorney’s office, and Amore.
The items stolen from the Boston Public Library would be difficult to sell because it would be easy to determine that they were stolen, Amore said.
“My message to the thieves would be: ‘You have not stolen a picture. You have stolen problems,’ ” Amore said. “The best thing would be to get them back to the library and hope it ends there.”