I think what might account for the study is not really about the anticipated reaction to a shooting. After all, as the article noted there’s hardly any shortage of blacks being killed in police confrontations (although at only 352 killings by police in 1998, it is pretty clear most police and most criminals will go their entire lives never seeing anyone shot).

I think the difference can be accounted for by that old racist adage “you all look alike to me”. If someone in your family suddenly went crazy, you’d probably notice something was wrong pretty fast. Your mom might even know something is wrong with you by just a glance! Yet if you saw a stranger on the street you’d probably need a few moments to determine if he was ‘wrong’ or just different.

Whites deal with other whites, in general, a lot. Even black police officers, unless they are operating in mostly black neighborhoods all the time, also have to deal with more whites in the general public than blacks. Spend enough time in a group and your ability to quickly see something that feels ‘wrong’ goes up. Don’t spend as much time and everyone ‘looks the same’ and your brain will require more time to make a snap judgement.