My take on this is that it shouldn't make sense, but that does not mean it always doesn't. As long as the possibility exists, in the extremely strange and warped political climate, especially of Georgia, for a pardon or a mitigation of the sentence, there's something to be said for a Federal backup. And if a successful civil rights charge occurs, perhaps it would have an effect on other things, such as the readiness of state prosecutors to sweep stuff under the rug, or of state juries to minimize future sentences, or even of good-old-boys to take certain risks. It's all theoretical, and all ought, I think, to be unnecessary in a case like this, but I can see why some people might consider it useful. My house hasn't burned down yet, and it probably never will, but it's insured.
I'm glad at least that their Fed. prison plea deal fell through. I suspect that the atmosphere in a Georgia prison will be a little stressful.