On the 23rd anniversary of the heist at the Isabella Stewart Gardner Museum in Boston, the FBI and federal authorities said they were close to nabbing the thieves behind the $500 million art theft.

“Today, we are pleased to announce that the FBI has made significant investigative progress in the search for the stolen art from the Isabella Stewart Gardner Museum,” said Richard DesLauriers, special agent in charge of the FBI’s Boston office, in a statement reiterating the $5 million public reward for information leading to the recovery of the artwork in good condition. “We’ve determined in the years after the theft that the art was transported to the Connecticut and Philadelphia regions. But we haven’t identified where the art is right now, and that’s why we are asking the public for help.”

Deslauriers said the thieves, who posed as police officers during the heist, were part of a criminal organization based in the mid-Atlantic states and New England, according to the Boston Globe.

The FBI has a strong idea as to where the art, including works by Rembrandt, Degas, Vermeer and Manet, may be located.

“[I]t’s likely over time someone has seen the art hanging on a wall, placed above a mantel, or stored in an attic. We want that person to call the FBI,” said Special Agent Geoff Kelly, the head investigator of the Gardner heist.

Robert Gentile, a 76-year-old Connecticut resident, had previously been questioned about the heist, but his lawyer said his information was not believed to be of value to the investigation, the Globe reported. It’s unclear exactly when Gentile was questioned or why authorities believed he might know where the paintings are.

Anthony Amore, Gardner’s chief of security, noted that the stipulations of the $5 million reward mean that whoever has the artwork doesn’t have to hand it over to authorities; the information leading to the recovery of the pieces is sufficient to get the reward.

“We hope that through this type of public campaign, people will see how earnest we are in our attempts to pay this reward and make our institution whole,” Amore said.

On March 18, 1990, the thieves gained access to the Gardner Museum, where they overpowered security guards, tied them up and stole 13 works of art valued at $500 million, according to the FBI.

“The recovery of the paintings will mark the close of a 23-year FBI investigation,” DesLauriers said. “The successful return of the paintings to the Gardner Museum would be the final chapter in one of the most significant art theft cases in the FBI’s history. And it is a result we would all welcome -- seeing these paintings returned to their rightful home.”

Anyone with information on the stolen artwork was urged to call the FBI’s hotline at 1-800-CALL-FBI or submit tips via the fbi.gov website.