With a 50/50 split, the chances are 0.78%, or just under 1 percent. If you consider an 85/15 white/black population distribution, the chances drop to 0.18%. So in a blind test, you're four times more likely to get a coin to alternate between heads and tails seven straight times, then you are to get W/B/W/B/W/B/W. It's not a statistical impossibilty, however. It's just roughly a 1 in 500 chance.
Actually, it's twice as likely for this to happen than to have 911 coming up in pick 3 in New York on 9/11. (Unless there were two drawings that day.)
Percentage of the population that's black in MD and VA is much higher than that. It's not all that unlikely that a randomly chosen group would be half black. What's really unlikely is the alternation.
I asked a LE type why the killer shot the woman instead of the man and he said it was because the Lady made the best target. When I picked my jaw off the ground, I realized it's probably true.