Preliminary findings from a post-mortem indicate a small fragment of a bullet struck Darfield gunman Donald Ineson in the back.
The 56-year-old was found dead in his car after a shooting incident involving his family and a standoff with armed police on Sunday.
District Commander Superintendent John Price confirmed shots were fired at the vehicle and entered at the rear, however, the investigation is still ongoing.
"The police investigation into the incident is ongoing as is the independent investigation of the Independent Police Conduct Authority," Price said.
"While the investigation is ongoing and still in the early stages police have established that one or more shots was fired by police after the deceased's vehicle had just been driven at officers, hitting and seriously injuring one of them."