Typically people don’t kill someone after they knocked them out. Most sane people run away or go get help once the threat has been stopped. They don’t usually kill a man while he’s already unconscious.
Either way, that’s apples to oranges compared to Zimmerman’s case. Trayvon Martin was beating Z’s head into the ground, and Z shot him when he had a chance to stop the threat. He did not stop the threat and then stop it permanently. Z, at the point, made an “in the moment” decision to save his own life. If he knocked Martin out and THEN shot him, that would’ve gotten him convicted because at that point, given what I understand about law and how I was following the actual trial (not the media’s portrayal, but HLN’s minute-by-minute unbiased updates), the jury would’ve found Z guilty beyond a reasonable doubt.
There is a huge difference between neutralizing threats and neutralizing THEN killing them.