It doesn't seem that the killing was intentional, not even criminal if it was an accident. Now, if it turns out that the manager studied martial arts, he might be held criminally liable. Fwiw, I don't think that the race/ethnicity of the parties matters. I do believe people become concerned when they think that the justice system minimizes or ignores an incident because of the victim's identity. When people believe that that happens, the facts of the case don't matter.
Anyway, it isn't hard to believe that someone died from being strangled. But, death from asphyxiation isn't quick. Ok, the airway can be ruptured irreparably; but, strangling to death takes a few minutes. I'm talking death, not unconsciousness. Unconscious people usually breathe just fine. So, at a minimum, the manager did more than what was necessary to incapacitate the alleged thief. And, some might argue that he (the manager) also had the responsibility to try to revive the guy. I wasn't there, but I just can't say the thief got what he deserved or 'oops, sorry about that.' After all, if all he took was toothpaste.... I dunno, it's just not a capital offense.
"A man is rich when he has time and freewill. How he chooses to invest both will determine the return on his investment."