Hickey's rifle went off as he placed it in a ranch utility vehicle, striking him in the body, said a sheriff's spokesman.
The autopsy of Hickey, 48, was completed Friday and found that he died of a single gunshot wound.
The incident was reported March 6 just after 9 p.m. at Hickeys home, 2855 Cloudy Meadow Road in Hidden Valley Ranch.
The Sheriff's Office said Hickey was found outside of his home by a family member on the night of the incident.
Someone called 911 just after 9 p.m. to report a person with a gunshot wound at Hickeys address.
Deputies and medics responded, but Hickey was pronounced dead at the scene.