DentThat said:
...Now in the event that you are brought before a judge and a jury, how would one be able to demonstrate that the shootings were out of self-defense and not murder; provided that there is no available witnesses?...
Beats me, and I am a lawyer. The thing is that these sorts of vague, open ended hypotheticals can't really be answered. The devil is in the details, and we don't have them here. A few observations, however --
[1]
DentThat said:
...The police arrive on the scene and see you leaving w/ the gun on you....
Why are you leaving? You have just committed multiple homicide, and flight equates to guilt. You stay, get out your cell phone, call 911 and tell them that you have just been attacked by three thugs and defended yourself. You ask for police and an ambulance. And then you wait.
What? You don't have a cell phone! Well get one. It's a necessary piece of emergency equipment.
[2]
Travis Bickle said:
In most states, it would be up to the prosecution to demonstrate that the shootings were not out of self defense....
Not quite. The prosecutor must prove the elements of the crime. If you're charged with murder, he must prove you committed the homicide with malice. If you're charged with manslaughter, he need only prove that you committed the homicide (that is that you killed the decedent).
Now here's the tricky part. If you are claiming self defense, you must admit the elements of the crime of manslaughter. You admit that you killed the decedent. Now the prosecutor doesn't need to prove that. You've admitted it.
So your defense is that even though you committed homicide, your act was justified. Now it is your burden to prove, or in some jurisdictions at least put forth evidence of, the elements necessary to support a claim of justified use of lethal force in self defense. And now the prosecutor needs to rebut your claim of justification.
To show the justified use of lethal force in self defense you must generally show that a reasonable and prudent person, in like circumstances and knowing what you know, would conclude that lethal force is necessary to prevent otherwise immediate, unavoidable death or grave bodily injury to an innocent. To demonstrate that there was indeed a real danger from the assailant, one must show that the assailant had (1) the Ability, i. e., the power to deliver force sufficient to cause death or grave bodily harm; (2) the Opportunity, i. e., the assailant was capable of immediately deploying such force; and (3) put an innocent in Jeopardy, i. e., the assailant was acting in such a manner that a reasonable and prudent person would conclude that he has the intent to kill or cripple. A person claiming self defense will need to be able to articulate why in the exact situation as it unfolded he concluded that lethal force was necessary based in the forgoing paradigm. And of course, the exact formulation can vary somewhat from jurisdiction to jurisdiction, the the forgoing will do in most cases.
What evidence do you have to support your defense? Well as the OP outlines the problem, his primary evidence will be his testimony. There may also be other evidence, forensic evidence, including the nature of the decedents' wounds, the position of the bodies, perhaps gunshot residue, etc. But the defendant will primarily have to rely on his testimony to make his self defense case. So now it becomes important that the jury believes your story.
That's how it is in real life.