Robert Gentile, an alleged mobster known as “The Cook,” has died of a stroke at 85. With him goes possibly the last chance of solving the world’s most expensive art heist, the 1990 Isabella Stewart Gardner Museum robbery. Gentile is believed to be the last known person to have possessed any of the stolen works of art. The heist, in which two thieves dressed as Boston cops sweet-talked their way into the museum after hours, claimed a haul of 13 paintings by artists like Rembrandt and Manet, worth an estimated $500 million.

When police searched Gentile’s home in 2010, they found a handwritten list of the artworks, annotated with estimated values. Gentile also revealed to cops during an undercover operation that he had access to two of the paintings, and could sell them for half a million dollars each. While authorities spent years pressing the geriatric gangster for information about the heist and clues as to the stolen art’s whereabouts, Gentile went to his grave denying any knowledge of the theft. The 13 artworks have never been recovered.