August 2, 2014 01:12 PM EDT
Keith Urban performs during the 2014 CMA Festival at LP Field on June 7, 2014 in Nashville, Tenn. 
FilmMagic
Keith Urban says he's 'horrified' by reports of a possible sexual assault at his concert last weekend south of Boston.
Eighteen-year-old Sean Murphy of Boston has pleaded not guilty to a rape charge filed after concertgoers told police they saw a possible assault on the lawn at the Xfinity Center in Mansfield. Bystanders captured the scene on cellphone cameras.
Murphy says the incident was consensual. The alleged victim told a bystander who intervened that she hadn't consented.
Urban made the statement in a Thursday Facebook posting, adding: "our hearts and prayers go out to all those affected. This type of behavior stands in stark contrast to the spirit of our shows."
Several dozen people were treated for alcohol-related illnesses at the July 26 concert.
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