No offense guys, but I think the OP is asking about the legal implications, if any, of taking a head shot especially as it considers the possible prosecution of actual or perceived wrongdoing on the part of the shooter. He is not asking about the tactic itself, lying to the police, whether it is good technique, etc.
Let me try to answer from the point of the prosecutorial review to the actual prosecution, if any, and what an expert witness would likely testify.
Step 1- After a shooting and the immediate investigation that ensues the case will be forwarded to the prosecutor’s office for review. This is not because the case is necessarily going to be tried, but simply a review of whether there is any sign of wrongdoing that needs to be looked at. This is standard procedure following a law enforcement or private shooting. The prosecutor first looks at the actions of the aggressor. They must answer this question. Would another reasonable person, in the same situation, believe that their life or the life of another was in imminent danger of death or grievous bodily harm at the time the shots were fired? If the answer to that question is a yes, you should not be charged.
It is important to note that it was the actions of the offender, and not the defender, that are in question at this moment in time. Therefore, if deadly force was justified than it would matter not whether you shot the person in the torso, the head, the pelvis, or dropped an anvil on their head from a 10 story building. The question of the force being used is not even considered until the actions of the aggressor are weighed according to the level of threat. If it was a deadly threat, your method of force should not be called into question. Therefore, a head shot could have been your first and only shot and would still not come into play.
Step 2- Let’s assume that there was a question as to the self defense issue and you are charged with a crime. Yes, the prosecutor is going to say anything and everything they can to win their case. They will say that you were out for blood, that no reasonable person would have done what you did, the works. At this point it is the job of the prosecutor to win the case. That’s why they are representing the state, and they get paid to win cases. Your judgment will be called into question, your weapon, the ammunition, your training, or lack thereof. No box will be left unchecked. It is enough to make you sick. I have seen it first hand and testified in such cases.
Step 3- As bad as step 2 sounds, if you were justified and assuming that you didn’t do anything to harm your position, i.e. make Clint Eastwood remarks, your case will not be extremely difficult to overcome. You will need a good defense attorney but just as importantly, this is exactly where an expert witness is indispensable to assert the reasonableness of your actions.
As an expert witness my testimony would likely include, but not be limited to, the following: 1) If force becomes necessary it should be the goal of the law enforcement officer (or civilian defender) to stop the threatening actions as soon as possible. 2) It is reasonable and common practice to aim center of mass of the target offered or selected by the shooter. This is the only way to ensure that threatening actions cease quickly. 3) If the first course of action proves ineffective, another course of action must be selected, i.e. alternate aiming point. 4) It is fruitless to continue to shoot at an area that has proven ineffective. If shots to the torso are ineffective a shot must, almost by demand for self preservation, be made at the head of the aggressor. 5) Even if the head were the first or only shot this is not unreasonable. The head may be the only target visible and even if it were not, it is a reasonable choice by virtue of being the most likely to stop the threatening actions quickly, perhaps saving additional lives.
I would continue to expound on the accepted practices of law enforcement from coast to coast, training hosted by law enforcement agencies, military, and reputable civilian trainers. I would cite actual cases of application including this infamous one by an Air Force Security Policeman
http://www.historylink.org/index.cfm?DisplayPage=output.cfm&file_id=8767
There would be no doubt left in the mind of the jurors that if deadly force were deemed necessary, that a shot to the head is reasonable by default. It does not matter whether the shot to the head was purposeful or occurred by reason of an errant shot aimed at the torso. I would finish by telling the jury directly that while nobody wants to see anyone killed, including an aggressor, that the lives of victims must come first. I would remind them that if they conclude that the client was acting in self defense, than it matters not the form in which that lethal measure took place.
Step 4- When you are acquitted of wrongdoing and reimbursed by the state for what was ultimately deemed self defense, send me a thank you note.