Prosecutors in Park City, Utah, are charging a man who they allege defaced two works of graffiti by Banksy, the elusive British street artist, with criminal mischief, a second-degree felony.

“It’s not every day I get to prosecute somebody for vandalizing graffiti,” Matthew Bates, lead prosecutor, told the Wall Street Journal.

According to prosecutors, David William Noll shattered the glass protecting the Banksy murals in Park City on New Year’s Eve, and then further damaged one of the works, an image of a boy praying on his knees, with dark brown paint. Noll faces a fine of up to $10,000 and up to 15 years in prison; according to Bates, a plea deal is being negotiated, with a hearing scheduled for September 15. Police say they have video of Noll at the scene of the alleged crime.

In a television interview with a local California station shortly after prosecutors charged him with the crime, Noll said he supports only “commissioned” graffiti.

The murals appeared on Park City’s main street in 2010, after Banksy attended the Sundance Festival on behalf of “Exit Through the Gift Shop,” the “mockumentary” he starred in and helped produce. Both local property owners, recognizing the value of a Banksy work, paid to protect the murals with glass, as others have done in cities around the world–one Brooklyn property owner even installed a metal gate and hired guards. Banksy’s solo works have sold at auction for as much as $1.3 million; a collaboration with artist Damien Hirst sold for $1.9 million.

[h/t the Wall Street Journal]