You are correct. But there are always going to be problems. If a prosecutor files charges, on his own, or because of a grand jury, most people will have in the back of their minds that the person must have done something wrong. That is the first prejudice the defense must overcome.
As to the bolded part, the prosecution will certainly try to introduce 20/20 hindsight into the evidence he presents. He is normally allowed to do so,
In a Grand Jury proceeding yes, but since the SCOTUS has clearly stated 20/20 hind sight is not a factor it really isn't allowed at Trial. However that is why, at least in my State, unless it is basically 100% obviously over kill etc., self defense cases rarely come to trial.
Which brings us to the underlined portion. Will the defense want the client to testify, or rely on witnesses? He may elect to take an affirmative defense, in fact, will almost certainly have to. Regardless, he will be testifying and subject to cross.
This is slowly changing however. in my State Self-defense is still an affirmative defense, however some States (Florida and Missouri come immediately to mind) the law has specifically changed this and it is actually the State's burden out of the gate also has to prove it was not self defense to either a Judge at a Preliminary Hearing or to a Grand Jury for indictment before it can proceed to trail and the same applies at trial.
How well can the accused articulate the circumstances that caused him to take the action he did. Just as importantly, can he continue to present his reasons that stand up under cross examination? Will his testimony be crippled in any way by the questions the prosecutor asks?
A lot of this though relies on whether the prosecution has witnesses to the contrary. On cross examination you can only ask questions on point to the answers given during direct testimony, of either the person currently on the stand or other witnesses, so this becomes a very much variable area.
Certainly the prosecution will make much of a defendant's martial arts training and background. How could he be afraid when he is a trained martial artist. After all, everybody knows they are trained to perform superhuman feats. And if he is a trained martial artist, isn't all his training to kill opponents, or at least if he fights, how does he control all that awesome power he has developed. He may bring in a teacher of any martial art to testify how the accused didn't follow proper martial arts training or worse, did, with deadly result.
This is actually becoming less and less a factor not only because of all the McDojo's around but also the classes taught at YMCA's etc. has greatly demystified the ideas of the Martial Arts. UFC has helped as well actually since you see people on TV all the time now talking about the "non-sense hokus pokus" of TMA's (not that that ever existed outside of movies but hey...)
Also the last bit is questionable as well. First the instructor would have to be certified as an expert witness, which can be no small matter. I once sat on the stand for well over an hour going over my credentials regarding narcotics investigations between direct and cross. Then the expert needs to be able to point to specifics, not only in the art itself but the facts of the incident. Is there video or a witness who is equally skilled in martial arts to be able to describe the techniques actually used? Simply saying "well a good martial artist would not have killed a guy" doesn't cut it. The Baltimore State Attorney found that out the hard way when her Expert on a "rough ride" had to admit on the stand he had no actual facts related to a potential rough ride in that specific case and that he was just "going off of stories he heard about what happens in Baltimore."
The bottom line as others have pointed out is that anyone who kills someone else may be prosecuted. The burden will then be on the survivor to prove he did so in self defense, which he must clearly articulate was within the allowable responses to the circumstances, under the law.
This is indeed true, which is why I tell people to educate themselves on the UoF Continuum if they plan to use Martial Arts, especially if they are going to use an art with a lot of weapons influence such as FMA. That said prosecutors tend to lean towards the person claiming self defense, so long as there isn't clear evidence of over the top activity such as kicking the guy when down in the fetal position, or something totally crazy like this
Byron David Smith killings - Wikipedia, the free encyclopedia when you set up an ambush and double tap them with head shots after you have already disabled them. Now this of course is not counting any political pressure to bring a case (which I suspect has bearinbg on the AU case), but history has shown those cases usually end in defeat for the prosecution.
Also, I don't think most of us here are lawyers. I am certainly not. Don't automatically see a post and think it sounds good, so you can follow that advice and not even go to court. It will probably get you into trouble.
I am not a lawyer either but I have worked many cases where claims of self defense were made, 2 of which resulted in death. One was a guy who was punched in a bar. When he punched the assailant in response, the assailant fell back and struck his head on the concrete floor, a screw from a plate in his head entered his brain causing death. The second was a man who was the victim of a strong arm robbery. He lashed out blindly with a knife striking the would be robber in the femoral artery. The suspect managed to run about 30 feet, collapsed and had bled out before EMS arrived. Charges were not filed by the DA in either case.
So at least in my case this is not speculation in the least, it direct experience with investigating cases and watching how the law plays out. Now you do have to keep in mind the UoF continuum, stop when the threat stops, AND know your State's laws on self defense etc. but as long as you truly educate yourself on these matters (and they are no small thing mind you, I just went through a mandated 6 credit hours of UoF classroom training and that was just a "refresher", there was no knew case law) you should be good to go.
