I've read all of the responses so far. Many of the responses are excelent - very informative. But, here is something I struggle with based on fiddletown's first comprehensive response: If a person happens to shoot and kill someone in self defense, it seems that an immediate decision must be made - report the incident and avail yourself of the self-defense affirmative defence, or not report the incident and make the authorities prove all of the elements of the crime.
If the shooter decides to report the shooting death, then he can expect to be arrested, spend some time in jail, have to bond out of jail (or if he can't afford to bond out continue to stay in jail until trial), if charges are pursued, be subject to trial, testifying and cross examination, and then roll the dice that he will not be convicted. The State basically is being handed a big portion of their case against the shooter on a silver platter.
If the shooter decides not to report the shooting death, perhaps because there are no witnesses or whatever reason, then he has no immediate concerns (legally speaking) unless and until he is somehow connected with the shooting. Then (I believe) the prosecutor will have to jump through all sorts of hoops to attempt to prove all of the elements of his case, if he even has enough evidence to get the shooter charged with the crime. If it looks like the prosecutor has all of the evidence to prove up his case, then the shooter could still acknowledge the shooting and avil himself of a self-defense claim, but that claim will be a weakened one.
There seems to be one element to this discussion that is missing that might entice a shooter who acted in self defense to call in the shooting. The police could look at the evidence and decide not to even charge the shooter with anything - if it's a clear cut case. Or could they? From what I've read, most folks who clearly shoot in self defense are never even arrested or charged with a crime. Is this correct, or am I wrong on this point? If there is a good chance that a shooter who clearly shot in self defense will not be arrested or charged, if he promptly calls 911 and cooperates with the police, then this is a huge incentive to take this path rather than the other. But, if you can plan on being arrested, charged, and tried regardless - I still think there is a decision to be made of whether or not to even report the shooting.