I tend to think that the "ethnic slur" accusation is just something trotted out by the perp to make it seem somehow excusable that he shot several people, some in the back, in an act of premeditated murder.
The ethnic slur allegation is nothing but a cheap excuse. I'm sure none of them could've seen what ethnicity he was, nor, I'm sure, would they have cared.
Very true --- imagine if everyone of Polish descent was entitled to shoot and kill a half dozen people every time they were called "pollacks" or whites could kill every time they were called "gringos" or "anglos" or "honkies". This is the height of political correctness ---- to try to justify cold blooded murder because evil Americans aren't welcoming other cultures.