Black Lives Matter when taken by Whites – a statistically rare occurrence.
Black Lives Matter even more if taken by Whites who display politically-incorrect symbols or hold politically-incorrect beliefs.
Black Lives Do Not Matter much at all when taken by other Blacks. This is a common occurrence. It never results in mass protests, Civil Rights demonstrations, demand for legislative change or any real outcry from the Black community or the US media/government.
White Lives Do Not Matter much when taken by Blacks. The US media/government frequently downplays or fails to report the race of the criminal in such cases.
In short, Black Lives Matter when useful in advancing a certain (anti-White, politically-correct) narrative. In other cases they do not. Where is the outrage from the Black community over this?