The thieves took 13 pictures from the museum, including three Rembrandts and a Vermeer. The total estimated value is $250 million to $300 million.
A spokeswoman for the FBI's Boston office told the Boston Globe Geoffrey Kelly, the agent now in charge of the investigation, has sent evidence to the FBI lab in Quantico, Va.
The museum, an Italian palace built by Isabella Stewart Gardner to house her art collection, was robbed by men who wore police uniforms to deceive the watchmen. The Gardner has offered a $5 million reward, and federal prosecutors have said they will not bring charges against anyone who surrenders the art.
Kelly's own theory is the thieves were local crooks who realized after the fact they had "committed the art heist of the century."
"They can't sell it. It's too hot," he said. "Taking the theory ... to its potential conclusion, now you've got these things so what do you do with them? Well, you hold on to them until the heat dies down, and here it is 20 years later, and it's just as hot.''