We're getting very far afield into self defense. So let me see if I can explain how probable case works and an affirmative defense works.
Evidence establishing probable cause to believe a crime has been committed and that you committed it is usually readily apparent (openly holding a Title II weapon, smoking your joint on the street corner, standing over a body with a smoking gun in your hand) or available to law enforcement using its various investigative tools (interviews, forensics, search warrants, etc.). Probable cause will support your arrest. It will also support charging you with the crime.
The prosecutor evaluates the evidence and decides if he has sufficient evidence to convince a jury beyond a reasonable doubt that you committed the essential elements of the crime (you possessed a Title II weapon, you possessed marijuana or you intentionally shot a particular person). If he decides he does, he goes to the grand jury and seeks an indictment (the expression of the grand jury's opinion that probable cause exists to believe you committed the crime) or he files a bill of particulars (or something similar called by a different name in the particular jurisdiction); and you are bound over for trial.
[Alternatively, evidence establishing your affirmative defense becomes apparent early on. For example, you promptly furnish you NFA paperwork or medical marijuana card. Or it's apparent from the circumstances that your use of lethal force was justified self defense. In such cases, it will go no further than the filing of a report.]
You go to trial presumed innocent. That means that it's the burden of the prosecutor to overcome that presumption of innocence by proving beyond a reasonable doubt that you committed the essential elements of the crime (you possessed a Title II weapon, you possessed marijuana, you intentionally shot a particular person). If he can't meet his burden of proof, you are entitled, under your presumption of innocence, to an acquittal.
So the normal defense tactic is to try to create a reasonable doubt that it was you, that you did it or that you did it intentionally. That will be pretty hard to do when you were seen holding the sbr, or when you were out in public openly smoking your doobie, or when you claim you had to shoot in self defense.
There is another class of defenses. These are called affirmative defense. If you are asserting one of these defenses, you are saying that you aren't guilty because you were legally entitled to do what you did. You were legally entitled to possess this Title II weapon or marijuana. You were legally justified in shooting this person who attacked and would have killed you if you had not used lethal force to stop him.
The principal evidence supporting your affirmative defense is within your control (your tax stamp, your medical marijuana card, your testimony about how you were attacked). And since this evidence is within your control, the law requires that you raise your affirmative defense and put forward the evidence to support it.
Does that clear things up for you?
ec4321 said:
...If an LEO shoots a suspect in an armed robbery, are they arrested?...
The LEO will be placed on administrative while the circumstances are thorough investigated. LEOs have been arrested and charged.
ec4321 said:
...I have to disagree on that, if you mean that in practice no arrests are made without PC. They can and do happen....
Unless the LEO is a rogue, he will not make an arrest unless he believes that he has probable cause. Sometimes there's a disagreement about that, and the question goes to a judge. The the judge decides.