The FBI believes it has identified the thieves who stole 13 artworks from Boston's Isabella Stewart Gardner Museum in 1990, in the costliest art theft in U.S. history.
The FBI said it believes the artworks, which are valued at a total of $500 million and include paintings by Rembrandt and Manet, were offered for sale by the thieves, but it does not know the art's current whereabouts.
"We have identified the thieves, who are members of a criminal organization with a base in the mid-Atlantic states and New England," Richard DesLauriers, special agent in charge of the FBI's Boston office, said on Monday.
DesLauriers said the FBI did not want to release the identities of the suspects because that could compromise its investigation.
The frames that once held works including Rembrandt's "Storm on the Sea of Galilee" and Edouard Manet's "Chez Tortoni" now hang empty on the museum's walls, in keeping with precise instructions about the museum's appearance that its founder left in her will.
The museum reiterated its offer of a $5 million reward for information that leads directly to the return of all the art.
"You don't have to hand us the paintings to be eligible for the reward," said Anthony Amore, the museum's security chief. "Today marks 23 years since the robbery. It's time for these paintings to come home."
The FBI called on anyone who had seen any of the missing art - which also includes works by Vermeer and Degas - to report it. (https://tips.fbi.gov)
"It's likely that over the years, someone - a friend, a neighbor or relative - has seen the art hanging on a wall, placed above a mantle or stored in an attic," DesLauriers told a press conference.
"We want that person to call us."
On the night of March 18, 1990, two men dressed as police officers arrived at the private museum's front door, and a security guard let them in. The thieves allegedly overpowered both guards, who were found duct-taped to chairs in the museum's basement the next morning.
The 13 stolen artworks included paintings, drawings, sculpture and a beaker.
The officials said they believed the artworks were taken to Connecticut and Philadelphia after the heist.
The Gardner Museum was founded by Isabella Stewart Gardner, an art collector who died in 1924. Her will contained very specific conditions on the running of the museum, including the arrangement of her collection and free admission to anyone named Isabella, a practice that continues today.
The FBI solved Boston's other long-running crime mystery in June 2011 when it found accused mobster James "Whitey" Bulger hiding in a seaside California community. Bulger, who is accused of committing or ordering 19 murders, was arrested on a tip that came in after the FBI launched a publicity campaign aimed at tracking him down. He had been on the run since 1994.