As the 20th anniversary of the Isabella Stewart Gardner Museum heist approaches, investigators are using the publicity to lure clues and witnesses, offering full immunity to anyone who helps return the 13 works that were stolen. The duo that broke in and lifted $500 million in goods—including works by Rembrandt and Vermeer—are of less interest to investigators than the goods themselves. The FBI now feels the immunity is key to getting good intelligence, as it weeds out the charlatans. “If someone had come forward a week after the robbery and said, ‘I wasn’t involved but I want the reward to turn it in,’ that would stretch credibility a lot,” an FBI investigator said. “But 20 years later, it is logical to think these paintings would have changed hands any number of times and wound up by now in an innocent person’s basement.” Police say they believe the artworks are most likely within a 100-mile radius of Boston and were taken by one of the city’s gangs. (And they’re pretty sure the “Dr. No theory”—an evil mastermind lording over the works in a hidden lair—has no relation to reality.) The museum is also offering a $5 million reward.