A bullet from an unknown shooter shattered a window at an Obama campaign office in Denver on Friday, leaving the window frame and the surrounding ground covered in glass shards but injuring no one.

The incident remains under investigation, with Denver police examining footage from surveillance cameras near the downtown office in order to identify possible suspects, the Associated Press reported.

Police spokeswoman Raquel Lopez confirmed to the AP that workers were inside the office when the afternoon shooting occurred.

A photo posted by Westword captured the aftermath of the shooting, showing a gaping hole in the window next to a U.S. flag and Obama campaign posters. The window was covered with plywood later in the day.

Lopez told the Denver Post that police had a description of a “possible vehicle of interest.�

Colorado is one of the most contested states in the upcoming election and President Obama, Republican challenger Mitt Romney and their surrogates have made multiple trips to the state in recent months.

A spokeswoman for the Obama campaign declined to comment on the incident.

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