Now, what I CAN see is this: if a person believes they were demonstrably charged wrongfully, they should have the OPTION of suing their accusers for defamation/lost wages, etc. This is an option, not an automatic suit, and allows for the possibility of the plaintiff losing the suit and eating even more legal fees. OJ Simpson would therefore not want to take this option, despite being found "not guilty," as regardless of actual guilt, there was plenty of evidence to justify his arrest/charges/trial. Someone who defended his wife from a rapist or who killed two gang members to save his son would have a greater chance of winning, and therfore be more likely to do this.
If the defamation/lost wages/wrongful charges suit is lost, the plaintiff should be held fully responsible for all legal and court fees resulting from that loss, in addition to whatever fees came from his criminal trial. Let a jury or judge decide on a case-by-case basis, because you just ain't gonna get a set of rules that will "take care of" every situation, and the cost of failing such a lawsuit should be enough to prevent spurious and frivolous claims (one would hope

Back to the topic at hand, I would suspect the reason this guy was charged in the first place was the ages of the dead gang members - 16 and 13. Someone in the prosecutor's office might have figured it was an easy "guilty" verdict, and pushed too hard. Or there could have been a politician putting the thumbscrews to the prosecutor to go ahead with the case, behind the scenes. The defendant himself may have made adrenalin-fueled conflicting statements, prompting an investigation. One of the dead punks' family members might have "known someone important." We simply don't know.
This situation, all legal bantering aside, should serve as a reminder to all of us that we do not lightly carry the means of our defense. Using our weapons in the defense of self and family will carry consequences, no matter the situation, and we should always be mindful of the worst that could happen. Things were bad for this gentleman; they could have been far worse. Yes, our lives and our loved ones' lives are worth that sort of trial (figuratively and literally), but we should never forget that the worst could happen to any of us. All it takes is an ambitious prosecutor and a capricious jury.
LawDog has a pretty good post on the subject here.