I once had reason to obtain legal advice from a local attorney regarding this issue in Georgia.
I was told to keep repeating,"I was in fear for my/their life/lives", and say nothing else.
IMO...Given the fact the perp in this case was obviously not going to stop being violent until forced to, one probably could've gotten away with using deadly force in this instance.
Now that I'm home from work, I have more time to give a better response.
I don't have the relevant code handy, but I have looked it up before to verify what lawyers and LE's have told me regarding justified use of deadly force here in Georgia.
Technically, citizens have just as much legal right as LE's to use deadly force.
The only requirement is that one be in fear for their own life, or the life of another person. And the law makes no distinction between being on one's own property or not, although the burden of proving "in fear for life" is much easier in one's home than in public.
I've been advised, if involved with a situation involving use of deadly force, say nothing to the police but,"I was in fear for my/their life/lives, and I need to speak to my attorney." And make damn sure you were in fear for your life before using deadly force.
I've also been advised that it's better to shoot someone dead than it is to cut them with a knife or beat them physically, and then they later die.
I do know that here in Georgia, clear cut home defense shootings never bring charges. Clear cut cases of armed robbers getting shot, by store employees or private citizens, never bring charges.
Not too long ago, an elderly man that owned a convenience store in Decatur, near Atlanta, shot and killed a robber with his trusty 12 ga., and there was never a mention of charging him.
About 12 years ago, a lady I know blew away(4 9mm in the chest, 2 in the head) a homeless guy that tried to enter her car after smearing crap all over her windshield.
Happened in a parking lot off Spring street, downtown.
She was never charged. It went quietly away.
In this case, while borderline, I believe no charges would've been brought against someone who used deadly force to stop this guy, as long as the shooter didn't carry on like Rambo, and showed some restraint.
Normally, one can't justify using a gun against an unarmed attacker, as in an otherwise normal guy who picks a fight at the bar.
But one could make a very good claim of fearing for one's life in this case.(Especially me, being a little guy.)
1. This guy was obviously mentally unstable. Probably just a shot out beggar who got pissed at the major's reply to his begging. Georgia juries are sympathetic to the shooter in cases when the deceased is a mentally deranged homeless perp that got violent.
2. The perp was obviously violent, without need of provocation, with no intention of stopping. At his size/weight, and with a mental issue, he is a deadly threat with just his hands against the average person.
At his size, he could snap a neck like a twig.
3. On a train in route between stations, there is no avenue for escape.
I live about 25 miles or so away from downtown Atlanta, and carry every second I'm within the city limits. If I had been on that train and witnessed the attacks, and no other alternative had presented itself, I would've shot him.
If the situation allowed it, I would try to wound him with a leg shot(As much as one can wound with a .45. "I tried to wound him by shooting him in the leg, officer. I can't help it that his leg came off."), before taking a kill shot.
But I wouldn't have hesitated, especially after he took out the old lady. And I feel confident I'd get away with it. If charged, it will be a state case with a state jury. Not an Atlanta jury.
Also, I can't yet verify this, but IMO, if one has a Georgia CCW,one can carry on MARTA. IIRC...With a CCW, you can carry anywhere but court, school, large public gatherings, and places that serve alcohol.
Hope this helps.