The most recent numbers I can find are for 2017.
Where the victim was black, the murderer was black in 88.45% of cases.
It's a similar situation with white murder victims, where the murderer was white in 80.21% of cases.
In that year, murder was the number 1 cause of death for black males under 45, with it being responsible for 35.3% of deaths in the under 19 age group, and 27.6% of all deaths in the 20-44 age group. For the same age groups when talking about white males, the figures are 5.2% and 2.8% respectively.
So, black people are murdered at a much higher rate than other groups, in terms of the number of murders per 100,000, but about 9 out of 10 are committed by other black people.
Sources: -
Current and previous listings-leading causes of deaths in the US
www.cdc.gov