A ghostly, veiled figure painted by Banksy on an emergency exit door of the Bataclan theater in Paris, the site of the 2015 jihadist terrorist attack that left 90 dead, stood quietly for seven months after it first appeared last June. But on early Saturday morning, thieves removed the entire door and took off with the work, which is believed to be Banksy’s tribute to those killed more than three years ago.

“We are today filled with a deep sense of indignation,” the Bataclan wrote on Twitter, confirming the theft. “The work of Banksy, a symbol of remembrance belonging to all—locals, Parisians, citizens of the world—has been taken from us.”

According to French media outlet LCI, an alarm went off at the theater around 4:25 a.m. on Saturday, but by the time police arrived, all they found was a screwdriver. Three hooded individuals allegedly left with the door in a van.

Works by the British street artist, whose identity is unknown, are becoming increasingly expensive, making them targets for thieves. Last June, a print valued at $34,000 was taken off the walls of a gallery in Toronto. Although the act was caught on camera, the work has yet to be recovered. In 2013, a mural was taken from the wall of a London discount store and wound up in Miami on an auction block.

But the mural outside the Bataclan theater was particularly symbolic to Parisians.

“This silhouette was made by the artist free of charge, it was an altruistic gesture in homage to the victims of the terrorist attack and their loved ones,” the mayor of the 11th arrondissement, François Vauglin, told LCI. “I find it very sad that people have taken it without thinking about what it represents.”

In a 2008 statement, the street artist expressed frustration with the removal of his work. “For the sake of keeping all street art where it belongs,” Banksy said, “I’d encourage people not to buy anything by anybody unless it was created for sale in the first place.”