Two paintings by the mysterious graffiti artist Banksy have been vandalised in the US town that hosts the Sundance Film Festival, one of them possibly ruined.
Brown spray paint covered a Park City, Utah, mural that depicted a young boy with a pink halo and angel wings kneeling to pray behind a can of pink paint.
The clear protective covering over the image had been shattered.
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The second piece, of a cameraman stooped to shoot video footage of a flower, was not defaced, but the covering had been cracked. The murals have become local points of pride since they appeared three years ago and police do not have a motive for the crime.
Surveillance footage captured a lone white man tampering with the art at about 2am on New Year's Eve.
Authorities are expected to release images of him to aid their search .
It is not clear whether the damaged mural can be restored, or how much the work was worth.
"Because of the fact that they weren't sanctioned, it could come down to a judge to determine the value of each of these," Sgt Jay Randall said.
The unauthorised art first appeared in 2010, around the time Banksy was in Park City for the Sundance debut of his documentary, Exit Through the Gift Shop.
The works initially prompted outrage by people who considered them unwelcome graffiti, according to Alison Butz, executive director of the Historic Park City Alliance.
But the city has come to embrace the murals.
The alliance features the work prominently on its website and the images are among the most-photographed sites in town, Sgt Randall said.
The elusive Banksy, who refuses to reveal his full identity, is known for silhouetted figures and spray-painted messages that show up in unexpected places.
His works have been sold at auction for as much as £670,000 each.