BOSTON (CBS) – The FBI says it knows the identities of the thieves involved in the 1990 theft of up to $500 million worth of art from Boston’s Isabella Stewart Gardner Museum.

WBZ NewsRadio 1030’s Ben Parker reports

READ MORE: 'It Was Shocking': American Flag Torn Down, Stolen From Pulaski Park In Boston

On March 18, 1990, two men disguised as police officers tied up the security guards and stole 13 objects, including rare paintings by Rembrandt, Degas, and Vermeer.  It was the largest property crime in U.S. history.

This Manet painting was one of the valuable pieces of art stolen in the 1990 heist. (Photo courtesy: FBI)

This Manet painting was one of the valuable pieces of art stolen in the 1990 heist. (Photo courtesy: FBI)

The suspects are members of a criminal organization based in the mid-Atlantic states and New England, it was announced Monday.  But they have not been named.

“Naming them would hinder the ongoing investigation to locate the art,” Richard DesLauriers, Special Agent in Charge of the FBI’s Boston office, said at a news conference at FBI headquarters in Boston.

Investigators now say they believe the paintings were taken to Connecticut and then Philadelphia where they were offered up for sale about ten years ago.

Since then, investigators’ knowledge of the paintings is limited.

So, the FBI is now using the same type of publicity tactics in Whitey Bulger’s capture to solve the robbery.  Targeted billboards and television advertisements led to the arrest of Bulger and his girlfriend Catherine Greig in Santa Monica, California in June 2011.

The FBI’s Gardner campaign will reintroduce the public to the 13 stolen works.

READ MORE: No Powerball Winner, Jackpot Climbs To $570 Million

Investigators are now asking the public for tips, believing someone has seen one of the paintings hanging on a wall or stored somewhere.

The museum is offering a $5 million reward for the return of the artwork, which is believed to be in good condition, according to Gardner Museum Security Director Anthony Amore.

U.S. Attorney Carmen Ortiz said the statute of limitations on the actual theft has expired, which means they can’t prosecute the two men who stole the paintings.

Author Ulrich Boser On Heist

But, Ortiz said, they could still file criminal charges against anyone who has the paintings or misled investigators.

“Immunity is available, it’s a strong possibility,” Ortiz said, if someone surrendered, but she would not offer “blanket immunity” without knowing more about the tips.

Ulrich Boser, who wrote the book The Gardner Heist, is hopeful that the art will be returned. “The people who have these paintings today seem like they might be willing to negotiate,” Boser told WBZ-TV. “Somewhere, someone knows where these paintings are today and we need that person to come forward.”

MORE NEWS: Coronavirus In Massachusetts: Today's Developments

The FBI has launched a new page on its website about the Gardner Museum theft,, to provide more information about the paintings and the case.