I'm sorry you have such a low opinion of the value of life. You actually said that if someone puts a hand on me I'll kill them. I'm afraid this is the kind of attitude the guy in the story had and if he had predetermined that he would kill anyone that bothered him he should be charged with murder.
I hope for his sake and his families this was a case of self-defense.
Seriously, think about this for a minute. This is real life, not the movies. I'm a pro-linebacker sized guy. If I landed a solid punch to your head or your neck, I don't care how big you are, there's a chance you could die. If you didn't die from that one punch, there's a very good chance you'd be knocked out, not able to breathe, or incapacitated in some other way.
There you are, hardly able to think, let alone grab your gun, with your fiancee in the seat next to you. You should have pulled out your gun before I punched you.
A gun is the great equalizer. Once you pull out a gun, if the other person is in the right state of mind, they'll back off, and that's the end of the conflict.
Obviously, we don't have all the facts yet, so this is just a complete guess at one possible scenario. They are arguing, and the drunk guy gets out of his vehicle and starts to approach the other guy's truck. The guy in the truck pulls out his gun. The drunk guy doesn't stop, and tries to open the door of the truck and pull the guy with the gun out. The guy with the gun shoots the drunk guy.
If that's what happened, I'd definitely call it self-defense.
A blood alcohol level of .19 is huge. I have a breathalyzer, and I've tested it thoroughly. At .19, I wouldn't recommend trying to climb a flight of stairs, let alone driving. His eyesight may have been so blurry that he didn't see the gun, or he just wasn't in the right state of mind to have the sense to leave the guy with the gun alone.
In my state (MN) whoever served him that much alcohol and let him drive would probably be found at fault and get a huge fine for something like this (not that I agree with that law).
We won't know what happened until the facts are out, but it kind of already looks like they are trying to railroad him.