( CNN ) -- The FBI said Monday it believes it knows who was behind one of the most significant art heists in the United States -- the 1990 theft of 13 precious works , once valued at $ 500 million , from Boston 's Isabella Stewart Gardner Museum . A couple of big catches in the announcement : The FBI did n't reveal the suspects ' names , said that the statute of limitations has run out so it ca n't charge anyone with the theft and that the artwork still has n't been recovered . The FBI said the suspects `` are members of a criminal organization with a base in the mid-Atlantic states and New England . '' The bureau also said it believes the artwork -- including paintings by Rembrandt and Vermeer -- was taken to Connecticut and the Philadelphia area and that the thieves unsuccessfully tried to sell some of the artwork in Philadelphia about 10 years ago . Charges still could be brought in the future against anyone holding the stolen masters . But authorities suggested the possibility of immunity would be considered should someone involved in keeping the art hidden away come forward and help the FBI to recover it . `` After the attempted sale ... the FBI 's knowledge of the art 's whereabouts is limited , '' the FBI said in a statement released Monday . At a Boston news conference , reporters pressed the FBI to name the suspected thieves , but officials declined , saying doing so might harm the ongoing investigation . The announcement comes on the 23rd anniversary of the theft , which the FBI says is one of the largest property crimes in U.S. history . In March 1990 two men posing as Boston police officers entered the museum in the middle of the night and tied up two watchmen . Among the the stolen items was a painting called `` The Concert '' by Johannes Vermeer , one of only 34 known paintings by the Dutch artist . Also pilfered were works by Rembrandt , Manet and Degas . Many view this as the single greatest art heist of all time . U.S. Attorney Carmen Ortiz said she has visited the Dutch Room at the museum several times and has seen the empty frames where the paintings once hung . `` I was reminded of the enormous impact of this theft , '' said Ortiz . `` I do remain optimistic that one day soon the paintings will be returned to their rightful place . '' The FBI says it 's releasing the new details of the probe in part to remind people of a $ 5 million reward for information leading to the recovery of the items in good condition . The FBI 's publicity effort will include a website devoted to the Gardner Museum robbery and the use of social networks and advertising on digital billboards in the Philadelphia region . Anyone with tip may call the FBI at 800-CALL-FBI or contact the agency online at https : //tips.fbi.gov . Mystery masterpiece revealed as Rembrandt self-portrait . CNN 's Devon Sayers and Susan Chun contributed to this report .
The FBI marks 23rd anniversary of huge 1990 art heist with new details of the crime . Agency says it has idea who stole artworks from Boston 's Isabella Stewart Gardner Museum . Score: 6