The black population in toto is far more violent than the white population, so any given violent crime is likely to have a preponderance of black perps. If you want to know why ask ten sociologists. They will give you answers with ten different slants and you can take your pick.
I happened by accident on the Dallas County Health Department statistics for STDs. Surprisingly, they reported the numbers by age group and then by race. Black STDs seemed to add up more than all the other races put together—extremely high. I blame this on the Democratic plantation—they have destroyed families and values.