According to Google Maps, there is a supermarket on the 1000 block of S Cesar Chavez Drive, "El Rey Market" -- link -- so it's still possible the initial reports of it happening at a supermarket could still be correct. Not saying that's where it happened, and I don't know Milwaukee very well, but that area doesn't look that bad. Then again, I've spent a lot of time in New York, so maybe my perspective is skewed a bit.