The reward for information about priceless paintings thought to have been stolen by Irish republicans is set to plummet within the next three days.

If you can provide details that help Boston’s Isabella Stewart Gardner Museum recover the pieces by December 31st then you’ll earn $10 million, if you wait until the New Year then you’ll only be given $5 million.

The 13 pieces were stolen in 1990 in what was then described as the biggest heist in US history; two men posing as Boston cops entered the building and handcuffed security guards - who wrongly believed they were under arrest. The men promptly grabbed as many pieces of art as they could and fled.

Read more: Irish republicans thought to be hiding $500 million worth of stolen American paintings in Ireland

Amongst the missing pieces are internationally acclaimed works such as Rembrandt’s Christ in the Storm on the Sea of Galilee and A Lady and Gentleman in Black.

Is this hanging in your neighbor's living room? Christ in the Storm on the Lake of Galilee, by Rembrandt

Is this hanging in your neighbor's living room? Christ in the Storm on the Lake of Galilee, by Rembrandt

Collectively, the 13 paintings are worth an estimated $500 million. 

Arthur Brand, a Dutch art expert, think it’s possible the painting are still in the hands of Irish republicans but have been smuggled from America to the Emerald Isle. In this case, they are most likely being kept in people’s attics and barns, or even hanging in people’s lives rooms whilst being passed off as copies. 

Boston’s Isabella Stewart Gardner Museum is offering a $10 million reward to help solve the biggest art heist in history: pic.twitter.com/vdysaekGTE

— CBS News (@CBSNews) July 12, 2017

“If someone in Ireland has the paintings, and was not directly involved in the theft, they can return them, claim $10 million and never be charged. That is a very good deal for everyone involved,” Brand told the Times of London earlier this year.

Law enforcement in Boston maintain the case is still on their books but no real progress in solving the crime has been made.

Read more: Iconic artworks inspired by the Irish Famine coming home to Ireland in 2018

Officials are, however, optimistic that the art works will eventually turn up.

Have you seen this painting?! Chex Tortoni by Manet

Have you seen this painting?! Chex Tortoni by Manet

"Typically stolen masterpieces are either recovered soon after a theft or a generation later. We remain optimistic that these works will ultimately be recovered,” the museum’s security director, Anthony Amore, told NPR earlier this summer.

If you have any information of the you can contact the museum, in confidence, by e-mailing, theft@gardnermuseum.org.

H/T: NPR

The Concert, by Vermeer.Wikimedia Commons