Have you ever wondered why when someone is shot dead and it is clear to everyone the victim died of the gunshot, the police will still want to conduct autopsy on the corpse. Have you tried to know why? Having known that the person was shot dead, is there any need for autopsy?
The police conducts autopsy, because assumption could prove them wrong, they have to be sure. Reason: certain things happen, but the obvious and assumed causes are not really the causes (Law of Coincidence). The person might have died just immediately the gun was shot, but another thing might have caused his death, not the gun shot, but life will always present to you, what you want to see.