Well, let's think on that one.
Consider the counterfactual - that homicide perpetration is evenly distributed and thus actual homicide perpetration should match share of general population. How then do we arrive at FBI UCR stats being what they are?
The easiest possibility would be the FBI disregarding what is reported to them and just making up numbers, but then you'd need a reason why bean counters tallying crime stats would bother and also it would be straightforward to test with a FOIA request.
Maybe the FBI is accurately reporting the numbers they are given, and a large number of police departments are simply reporting a bunch of black folks committing homicide when that's not happening? That could also be tested using public records (comparing numbers reported to FBI against actual cases), but would be a more involved process unless you have particular districts that you feel are more likely to be fudging the numbers.
Maybe it's racially biased over/underpolicing? Except we're talking about homicide, and it's hard to overpolice homicide (you've only got so many corpses to work with), which means underpolicing when white folks commit homicide. But by the same stats 4 in 5 homicides have killer and victim of the same race, which would mean police just ignoring it when white people are killed, which doesn't sound very white supremacist of them.
Maybe there are white people killing black people and successfully framing other black people for the crime? That could happen, I guess. It would require massive incompetence or overt racism on the part of police, and have to stay secret, and have to be happening at a truly massive scale (we're talking thousands of cases every year for as long as we've been keeping the stats). Which feels unlikely just in sheer scale.
You know what I think is likely? That the stats gathered are accurate, and more homicide is done both by and to black folks because a lot of homicide is gang violence and at a national scale the prime gang recruiting demographic is poor young black men. There are statistical methods by which this too could be tested, but it would be more of an ordeal than the others, and merely admitting that law enforcement statistics regarding race might be accurate probably denies you funding outright.