This will be kind of long, but I think it's important. Too many people have extravagant and unrealistic expectations of Castle Doctrine/Stand Your Ground laws. People need to understand what they mean and how they work. They can help someone who has legitimately used force in self defense establish that his use of force was justified, but
they are not
"licenses to kill", "get out of jail free cards", or "commissions as a freelance vigilante."
I. How Pleading Self Defense Works
In general, if you're accused of a crime it's up to the State to prove your guilty beyond a reasonable doubt. But things work a little differently if you are pleading self defense.
 The prosecutor must prove the elements of the underlying crime beyond a reasonable doubt -- basically that you intentionally shot the guy. But if you are pleading self defense, you will have admitted that, so we go to step 2.
 Now you must present evidence from which the trier of fact could infer that your conduct met the applicable legal standard justifying the use of lethal force in self defense. Depending on the State, you may not have to prove it, i. e., you may not have to convince the jury. But you will have to at least present a prima facie
case, i. e., sufficient evidence which, if true, establishes that you have satisfied all legal elements necessary to justify your conduct.
 Now it's the prosecutor's burden to attack your claim and convince the jury beyond a reasonable doubt that you did not act in justified self defense.
Let's go through that again.
In an ordinary criminal prosecution, the defendant doesn't have to say anything. He doesn't have to present any evidence. The entire burden falls on the prosecution. The prosecution has to prove all the elements of the crime beyond a reasonable doubt.
If the crime you're charged with is, for example, manslaughter, the prosecution must prove that you were there, you fired the gun, you intended to fire the gun (or were reckless), and the guy you shot died. In the typical manslaughter prosecution, the defendant might by way of his defense try to plant a seed that you weren't there (alibi defense), or that someone else might have fired the gun, or that it was an accident. In each case the defendant doesn't have to actually prove his defense. He merely has to create a reasonable doubt in the minds of the jurors.
But if you are going to be claiming self defense, you will wind up admitting all the elements of what would, absent legal justification, constitute a crime. You will necessarily admit that you were there, that you fired the gun, and that you intended to shoot the decedent. Your defense is that your use of lethal force in self defense satisfied the applicable legal standard and that, therefore, it was justified.
So now you would have to affirmatively present evidence from which the trier of fact could infer that your conduct met the applicable legal standard justifying the use of lethal force in self defense. In some jurisdictions, you may not have to prove it, i. e., you don't have to convince the jury. But you will at least have to present a prima facie
case, i. e., sufficient evidence which, if true, establishes that you have satisfied all
elements necessary under the applicable law to justify your conduct.
Then it will be the prosecutor's burden to attack your claim and convince the jury (in some jurisdictions, he will have to convince the jury beyond a reasonable doubt) that you did not act in justified self defense. And even if you didn't have to prove self defense (only present a prima facie
case), the less convincing your story, and your evidence, is, the easier it will be for the prosecutor to meet his rebuttal burden.
II. How a Castle Doctrine/Stand Your Ground Law Can Help
Since this particular case arose in Florida, we'll look specifically at Florida law. However, all the self defense/Castle Doctrine/Stand Your Ground laws I've looked at are pretty similar.
 In general, under Florida law the use of lethal force can be justified as provided in Title XLVI Florida Statutes, Section 776.012
...a person is justified in the use of deadly force and does not have a duty to retreat if:
(1) He or she reasonably believes that such force is necessary to prevent imminent death or great bodily harm to himself or herself or another or to prevent the imminent commission of a forcible felony; or
(2) Under those circumstances permitted pursuant to s. 776.013.
 So if you claim your use of lethal force in self defense was justified, you will at least need to put forth evidence that the requirements of 776.012 were satisfied.
 The Florida's Castle Doctrine/Stand You Ground law at Section 776.013
helps by providing, among other things:
(1) A person is presumed to have held a reasonable fear of imminent peril of death or great bodily harm to himself or herself or another when using defensive force that is intended or likely to cause death or great bodily harm to another if:
(a) The person against whom the defensive force was used was in the process of unlawfully and forcefully entering, or had unlawfully and forcibly entered, a dwelling, residence, or occupied vehicle, or if that person had removed or was attempting to remove another against that person’s will from the dwelling, residence, or occupied vehicle; and(2) The presumption set forth in subsection (1) does not apply if:...
(b) The person who uses defensive force knew or had reason to believe that an unlawful and forcible entry or unlawful and forcible act was occurring or had occurred.
 A presumption is a rule that affects evidence and burden of proof in court. Ordinarily, one who asserts something in court will have the burden of proving, by presenting good evidence, that certain facts supporting that assertion are true. But sometimes the law might allow one of those facts to be accepted as true without specific evidence of that fact if the party with the burden of proof shows that certain other facts are true. So the party might be entitled under a rule of law to have fact A presumed to be true if facts B, C, and D are shown to be true, even if the party produces no direct evidence that fact A is true.
 So you can establish that your use of lethal force was justified, thus satisfying 776.012, if --
- You can show that
- The person you used force against was, "...in the process of unlawfully and forcefully entering, or had unlawfully and forcibly entered, a dwelling, residence, or occupied vehicle, or if that person had removed or was attempting to remove another against that person’s will..."; and
- You, "...knew or had reason to believe that an unlawful and forcible entry or unlawful and forcible act was occurring or had occurred...."
- None of the exceptions in 776.013(2) apply.
And if you can do that, you don't have to specifically establish that you believed, "...that such force is necessary to prevent imminent death or great bodily harm to himself or herself...."
 But note that you don't get the presumption automatically. You need to show that the conditions that create the presumption exist. That might be easier than showing a fear of imminent death or great bodily harm, but you still must do some work to establish your claim of justification.
 And in the law, any available presumption is rebuttable. That means that even though one may be entitled to the benefit of a presumption as to a certain fact, the other side may try to prove that fact is not actually true. So, for example, even if you might have been entitled to a presumption that you were reasonably in fear for your life, the prosecutor could put on evidence and try to show that under the particular circumstances, a reasonable person could not have been reasonably in fear for his life.
III. The Bottom Line
Every Castle Doctrine/Stand Your Ground law has conditions, in general similar to those under the Florida statute, that you will need to show have been satisfied in order to be protected under those laws.