It’s been nearly 24 years since 13 masterpieces worth a cumulative $500 million were stolen from Boston’s Isabella Stewart Gardner Museum, but some of the boosted paintings have been seen since, according to the FBI. In his first TV interview, with Boston’s FOX 25, special agent Geoff Kelly—the lead FBI investigator on the Gardner heist case for the past 11 years—says some of the works were seen as recently as 2000. At the time, according to sources the FBI considers credible, the paintings by Vermeer, Rembrandt, Degas, Manet, and more were in Philadelphia and were being offered for sale.

“From expanding our investigation and expanding the world in which we’re investigating we’ve identified a number of individuals who reported that they’d seen the paintings being offered for sale in Philadelphia,” Kelly says.

In the interview Kelly also names three key players he believes to have been involved with the theft and subsequent selling off of the works: Carmello Merlino, Robert Guarente, and Robert Gentile. While Merlino and Guarente are dead, Connecticut-based Gentile has been interrogated as recently as last year over his friendship with Guarente—who has long been believed to have known who carried out the theft, if he wasn’t directly involved in it. In spite of the FBI’s insistence to the contrary, Gentile has denied knowing anything about the Gardner heist.

“When this case initially went down the suspect list was pages long and over the last 24 years we’ve really been able to whittle that list down,” Kelly says. “We do know that Mr. Gentile would possibly have information that could help us in the recovery of these paintings and that’s why we approached Mr. Gentile for his assistance.” That didn’t pan out so well, though, as Kelly notes that Gentile “claimed to have no knowledge of the Gardner heist or the stolen artwork.”

There is a $5 million reward being offered for the return of the works, as well as immunity from the U.S. Attorney.