As usual, I agree with Lawdog. The answer varies. I have edited my comments at
http://www.thefiringline.com/forums/showthread.php?threadid=64983 to fit this thread.
Consider these factors in resolving your dilemma:
1. If you don't say a word, you may lose valuable evidence. There may be artifacts around the scene that are relevant to you but not immediately apparent to the police. By the time you get a lawyer on board, the scene may have been processed and exculpatory evidence lost, and the ability to enlist the aid of the police in support of your theory, or to establish your credibility, also may be lost. If you get a lawyer, make sure he/she acts quickly to preserve evidence, but it's not as good as having the police as your witness.
2. Police have spouses, significant others, friends, kids, parents, etc. Generally, in all but the most rabid anti-gun/PC/paternalistic places, the police will go out of their way to exculpate a person they believe to have acted legitimately in self defense. I guess I am fortunate enough to have lived in places where police don’t have a problem with good guys turning the table on bad guys. I know one person who was congratulated by police after she shot a guy (probable career criminal) who followed her and her sister into the house with obvious nefarious intentions. I also have seen police CLEAR suspects as a result of voluntary interviews, contrary to popular belief.
3. Your decision may turn on the circumstances of the particular case. If it's a crime being committed in your house by a total stranger who forcibly entered with a deadly weapon at 3 a.m., it's going to look different to police and prosecutors than if it's a re-escalation of an argument that took place in a bar involving your ex-spouse's new "friend." I have seen some situations that were so squeaky clean that police would have wondered why the good guy was stonewalling, and others where people were whispering, and the people involved definitely should shut up.
4. There are 4 possibilities:
a. you don't get arrested and you don't get prosecuted
b. you don't get arrested immediately but you later get arrested and prosecuted
c. you get arrested but you don't get prosecuted
d. you get arrested and you get prosecuted
The less you say the more likely you are going to get arrested, because the police will only be looking to the physical evidence and what the bad guy/witnesses say. Be prepared to go to jail. The less you say the harder it is to convict. Talking immediately could help you on the front end and burn you on the back end. It is a major dilemma. If you live in a place where you can be assured of being arrested, then there's less reason to talk (outside of loss of evidence concerns) because you're not going to beat the ride under any circumstances. If the place where you live has a really bad jail, you may not want to spend a minute in a holding cell with real criminals accused of murder, rape, etc., because that's how you'll be treated if arrested for shooting someone.
5. Self defense or justification is a defense to something that ordinarily would be a crime. So, admitting facts that amount to shooting someone does establish the elements of the crime, whether aggravated battery or homicide. OTOH, even if you don’t admit what happened, if the police show up at your house and you, your gun, and a bleeding bad guy are there, the lack of that statement isn't really going to save you much grief. The reality is that you have intentionally shot someone, and you were relying on your defense. Are you really planning to wait until the prosecution proves a homicide at trial before you decide to say "OK, so you have a point, but I have a defense to it"? It is a good idea to talk to a lawyer in your state in advance on burden of proof and other procedural issues.
6. If you wish to speak to a lawyer, approach it from the standpoint that this was a traumatic occurrence, that you are unfamiliar with the procedures, and that you would like to get some advice, rather than taking the approach that you know your rights and want to talk to a "suit." Also, if you are traumatized, go to the hospital and seek medical care. Yes, you are a victim even if you don't have a bullet hole in you. This delays questioning, allows time to get your composure and to get a lawyer, etc. You should NEVER talk until you are relaxed, comfortable, rested and READY, because of the consequences.
7. Regardless of your decision on speaking to the police, UNDER NO CIRCUMSTANCES should you speak to anyone other than persons who cannot be forced to testify if you object, such as your duly employed lawyer (attorney-client privilege) or other persons governed by your particular state law (e.g. husband-wife and clergy privileges in many states). (There haven't been any parent-child privileges where I have lived.) The police are going to interview everyone with whom you spoke about the incident, and if your multiple stories don't match, even for innocent reasons, it could work against you. Cruiser, the husband/wife privilege is usually 2 distinct privileges. One is the defendant’s right to prevent the non-defendant spouse from testifying (with exceptions, such as if the non-defendant spouse is the victim). Check the local law of your jurisdiction.