The Isabella Stewart Gardner Museum in Boston is famous for housing some of the most important works of art in the United States. Since 1990, the museum has also been synonymous with something else—the art heist that took place there, which is often referred to as the "crime of the century." Should you happen to have any information on the heist, well, now is the time to fess up—after December 31st the reward for information leading to the recovery of the paintings will be cut in half, from $10 million to $5 million.

As Camila Domonske reports over at NPR, after the disappearance of 13 paintings—including works by Manet, Degas, Vermeer and Rembrandt—the museum first issued a $1 million reward. Eventually, the reward was boosted to $5 million. Then, after years with no solid leads the wherabouts of the art works, the museum decided to try and entice someone with a sliver of knowledge into coming forward by bumping the reward to $10 million for 2017.

Anthony Amore, chief investigator of the theft for the museum, tells Domonske that the museum isn't particularly interested in fingering who did the deed. In fact, the FBI believes the heist was committed by two men associated with the mob, but have no concrete evidence, and the statute of limitations has already run out. As CBS News reports, both suspects are now deceased and the FBI believes the paintings moved through mob connections in Connecticut and Philadelphia, which is where the trail went cold. The last living person of interest in the case, reputed Connecticut mobster Robert Gentile, now 81, is currently in custody for gun charges (he made the news recently for accusing the government of cruelty for shuttling him between prisons for medical treatment). In 2010, a widow of one of Gentile's mafia associates told the FBI she saw several of the paintings in Gentile’s possession. He subsequently failed a polygraph exam in which he denied knowledge of the paintings’ whereabouts. Still, he is not talking and his legal team claims he is suffering from a form of memory loss or dementia.

The museum has left up the empty frames of the stolen works for almost three decades in the hopes that the paintings would return. “I am focused like a laser beam on one thing and that is recovering our stolen art and putting it back on the walls here at the museum, where it belongs,” Amore says. “We have received a few good calls with important information, and we hope to receive more before the end of the year.”

The heist itself was a work of art in its own right. According to the museum, on the night of March 18, 1990, two men dressed as police officers rang the museum buzzer telling the guard, Rick Abath, that they were called about a disturbance at the museum. The night guard let them in through the employee entrance. The thieves told him that he looked familiar and that they had a warrant for his arrest. Abath obeying their orders, got up from his desk, where the only security alarm button was located. The two men then handcuffed and tied up Abath and his partner and put them in the basement.

Then, the thieves spent 81 minutes in the museum, primarily in the Dutch Room cutting Rembrandt's “A Lady and Gentleman in Black” along with the artist’s only seascape, “Christ in the Storm on the Sea of Galilee," from their frames. In total, 13 works of art were stolen that night, totaling an astronomical price tag of $500 million.

For his part, Abath still feels terrible about the event. “I was playing in a band and working night shift at the museum,” he told NPR’s Story Corps in 2015. “I was just this hippie guy who wasn't hurting anything, wasn't on anybody's radar, and the next day I was on everybody's radar for the largest art heist in history.”

As the heist was so high-profile and the works so famous, it’s unlikely that the thieves were able to sell the pieces outright. But in recent years, famous artworks have been used as internal payments or bonds within organized crime, something that is dramatized in Donna Tartt’s Pulitzer-prize winning novel, The Goldfinch.

Writing for CNN after the reward was first doubled, art historian Noah Charney predicted that the extra payout would not see results. Despite some fine investigative work and several well-researched books on the crime, the general consensus is that anyone who knows where the paintings are hidden is probably dead, and it’s not clear if anyone living knows their whereabouts. Charney writes that he is confident the art works will one day be found, but likely far in the future by someone poking around an attic or crawlspace or storage locker, not recovered in a triumphant FBI raid.