Aurora Police say it happened on Granby Way near North Chambers Road.
When police arrived, they found a man suffering from a life-threatening gunshot wound. He was taken to a local hospital and his condition has not been released.
Police say the man who fired the gun was taken into custody. According to police, 25-year-old Barton Enoch of Loveland, is being held in lieu of a $50,000 bond for investigation of second-degree assault.
Investigators say six members of the Marine Corps Reserve were at the condo, but did not specifically say if the victim was a member of the military.
Police are looking at the possibility that alcohol may have been involved.
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