Attack an insider, kill an outsider? I've read that animals as a rule exhibit non-lethal violence toward members of the in-group and lethal violence toward outsiders, and I wondered if it might apply to human races.
I found rates of within- and cross-race aggravated assaults and homicides for 2006 and looked to see if assaults turn into murders more frequently if the attacks are cross-race. Here are the ratios of aggravated assaults to homicides for different combinations:
Ratio of aggravated assaults to homicides
Just to make sure you're interpreting those numbers right, using the first one, read it as, "For whites attacking whites, you'll have 172 aggravated assaults for every murder." So the lower the number, the more likely someone ends up dead.
So, you can see that black-on-black violence is the deadliest; white-on-white the least so. The second deadliest is black on white, so the chance of death is highest when the perpetrator is black.
Whites are somewhat more likely to kill a black victim than a white one, so this is consistent with the hypothesis, but a black attacker is much more likely to finish off the victim if he is also black--a non-supportive finding.
I should mention the important fact that a great deal of serious violence is mutual combat. The story here seems to be that black participants in violence--whether they end up the victim or the aggressor--are more intensely violent than whites. Have two whites go at it, and you get few deaths. Insert a black as the victim or especially the offender, you get more deaths. Insert two blacks, and the chance of murder jumps even higher.
Does this seem right, or are there other ideas?