there were data classifying by race of  murderer AND victim, black-on-black is also disproportional. 
https://ucr.fbi.gov/crime-in-the-u.s/2018/crime-in-the-u.s.-2018/tables/expanded-homicide-data-table-6.xls

another clue: in Brazil 80% of murders are drug-related, including gang wars, addicts commiting crimes, debt 'settlements', etc.
I do not know about the USA, would it be close?