(NECN: Alysha Palumbo - Boston) - Monday marked 23 years since thieves pulled off one of the largest art heists in history at Boston's Isabella Stewart Gardner Museum -- swiping 13 works of art valued at half a billion dollars.
Now federal investigators say they're confident they've identified the thieves...although they're not naming them.
Special Agent in Charge FBI Boston Division Richard DesLauriers said, "With a high degree of confidence we believe those responsible for the theft were members of a criminal organization with a base in the mid-Atlantic states and in New England."
Last year FBI agents searched the Connecticut home of reputed mobster Robert Gentile, reportedly in connection with the art heist.
But investigators would only say they've determined the art was transported to Connecticut - as well as Philadelphia - even specifying that some of the art was offered up for sale in Philly about a decade ago.
U.S. Attorney Carmen Ortiz said, "The statute of limitations has run on charges for example on the actual taking of the paintings at that time, but there's potential criminal liability for anyone who's in possession of stolen property or concealing the paintings."
Ortiz says her office is willing to offer immunity if someone comes forward with credible information on the stolen paintings and sculptures.
Museum Security Director Anthony Amore says their focus is not on punishment, but on returning the priceless works of Rembrandt, Degas, Vermeer and others to their rightful place.
Amore said, "Imagine never hearing Beethoven's Fifth Symphony again, or never seeing Hamlet performed again."
Investigators say they believe the artwork may have changed hands several times over the past two decades.
DesLauriers said, "It's likely over the years that someone - a friend, neighbor or relative - has seen the art hanging on a wall, placed above a mantel, or stored in an attic, we want that person to call us."
The museum has offered a $5 million dollar reward for information leading to the recovery of the stolen artwork, in good condition.
If you have information on the location of this art, you can contact the FBI at 1-800-CALL-FBI or go online to https://tips.fbi.gov
The full press conference can be seen here.