Why is it a racist attack? The simple fact that the victim is white and the assailants are black not doesn't make it racist, does it? What added factor do you see ? Do you know the motive for the killing? What evidence is there that it was only that he was a white man and this gang was out to kill a white man, without anything more? Or do you think that racism is so rampant that no white man is safe from being killed because of the colour of his skin , therefore this must be motivated by that?
All you know is that a number of black men chased and killed a white man. Now that may be for a number of reasons; he might be suspected of being an informer, he might belong to a rival gang, he might be a drug dealer on their turf... and so on. One thing is certain: anyone informing on the killers, would be unwise, just as anyone would be if he or she informed on a Mafia gang or any other which is capable of murder or severe violence. And those who really know are the killers themselves.