Actually, you don't know the percentage of homicides committed by blacks or by whites.

First of all, there are unsolved homicides.

Secondly, just because someone is charged with, or even convicted of, a homicide, it is not necessarily a fact that they committed that homicide.

Some time back, one of those sets of statistics came out for New York City, from which a friend of mine concluded that 94% of homicides in the city were committed by blacks. When I dug into the data, it turned out that percentage included all homicides which 1) were in black neighborhoods, or 2) for which a black person was brought in for an interview, whether the person was charged with or convicted of the crime or not.