Why is it that you jump back and forth between qualifying/modifying your statements with urban blacks.
There are two different topics here. When I'm talking about serial/spree/mass killers, I talk about blacks in general, as that's the data we have. When we talk about street gun violence I clarify that we are talking about urban blacks, and that there isn't any indication that there is a problem with blacks outside major cities.
On the serial/spree/mass killer topic the information we have is that the differences between races are small and likely explained by socio-economics. On the street gun topic there is clearly a very large racialized element to the crime not explained by the socio-economics. Victims of the Washington sniper were unrelated to the shooter, as with the Colorado shooting. Even the Virginia Tech case, where the guy attacked his own school, the people he actually shot were mostly strangers within that institution.
If murder is a non random event you are more likely to be killed by someone you know.... most of the black fearing people on terb probably have little to no black friends.
It's less clear that spree/serial/mass killers are likely to know their victims. There are many cases where there's some association, the killer attacks his own school/workplace/etc., but it's also true that a lot of them kill strangers.
For street gun violence, the high rate of crime by blacks implies that, even though most of it is black on black, that is still the largest source of risk for everyone else. You are more likely to be killed on the street by a black man than by any other race, even if you are not black.
Outside of street crime, your point is correct. Most murders are domestic and you're most likely to be murdered by your own family, following that by a friend or business partner.