I've not personally heard about this, but two things spring to mind, other people clearly have so I can't see it's being "covered up", and secondly just because it was five people of one race killing one person of another ,does not mean it was NECESSARILY racially motivated. It may well be, but it's not automatic is it?
For example, assume I thought a black guy had raped my daughter. Myself, my brother, brothers in law and sons all go out, find this bloke and kill him, despite the fact that he's black and we are white, that is NOT a racially motivated murder, so before I comment seriously, does anyone have a link please to what we are supposed to be discussing?