Almost exactly 29 years ago, two men disguised as police officers weaseled their way into Boston’s Isabella Stewart Gardner Museum and started removing prized artworks from the wall. They made off with 13 famous paintings and sculptures, representing a value of more than $500 million. It remains the largest property theft in U.S. history, but no one has ever been charged in connection with the heist.

Now, as Smithsonian reports, the last living person who may have first-hand knowledge about the heist will be released from prison this Sunday after serving 54 months for an unrelated crime. Robert (Bobby) Gentile, an 82-year-old mobster who was jailed for selling a gun to a known murderer, has been questioned by authorities in the past. In 2010, the wife of the late mobster Robert (Bobby) Guarente told investigators she had seen her husband give several of the artworks in question to Gentile—a good friend of Guarente’s—eight years prior.

A 2012 raid of Gentile’s home also revealed a list of black market prices for the stolen items. Previous testimony from other mob associates—coupled with the fact that Gentile had failed a polygraph test when he was questioned about the art heist—suggest Gentile might know more about the crime than he has let on. For his part, though, Gentile says he is innocent and knows nothing about the art or the heist.

The FBI announced in 2013 that it knew who was responsible for the museum heist, but would not reveal their names because they were dead. Still, the whereabouts of the artworks—including prized paintings by Rembrandt, Manet, Vermeer, and Degas—remain unknown. The museum is offering a $10 million reward to anyone who can provide information leading to “the recovery of all 13 works in good condition," according to the museum's website. A separate $100,000 reward will be provided for the return of an eagle finial that was used by Napoleon’s Imperial Guard.

[h/t Smithsonian]