How was Killen convicted of Manslaughter`

I spend half of my murder trials thinking of ways to get a manslaughter out of a murder (this includes offers to plead to manslaughter, often to the maximum of over 20 years). Most often, these attempts fail. So, I'm wondering, and perhaps someone can tell me, how did Killen get a voluntary manslaughter out of his particular set of facts (I understand, by the way, that just about any prison sentence is probably a life sentence for him, and that as compromises go, his is not particularly helpful, but still, you never know what may happen down the road to let him out at some point, or what a judge may do with a manslaughter conviction coupled with his age - he may not get the rest of his life in prison after all)?

Let's see, if I recall the case correctly (admittedly, most of my facts come from reading recent newspaper accounts, accounts from classes I took in college, and sadly, the movie Mississippi Burning), the local Klan stopped these three guys on the road and lynched them, then buried the bodies. Did the defense put up a defense of "heat of passion," that somehow the local Klan was so inflamed by federal interference into their local customs that this amounted to a heat of passion? If so, how does that square with his defense that he wasn't there that day? Did they put up a defense of "I wasn't there, but if I was I was acting under extreme heat of passion?" I had always considered those to be losing arguments, and had counseled my clients to pick one - heat of passion/self-defense or alibi, but not both. Maybe I need to reconsider.

Or, maybe, the old south really lives on in some form or fashion. Was this jury trying to cut this guy a break because he was a good old boy that had the right idea but was a little misguided in the way he went about it? I dunno. I'll read more to try and get some insight. If anyone knows, I'd be interested in their thoughts. Please respond to the comments so I can start to understand. Was this a legal decision, or was it a political one?

As a backdrop, I have to believe that those southern conservatives that run Washington these days won't rail against this verdict and call the jury "kooky" the way they do against things like the Michael Jackson verdict, or, perhaps a closer analogy, the first Menendez jury (where the jury hung between murder and manslaughter).

UPDATE: Thank you to Jonathan Soglin for pointing this out, but I guess it shouldn't surprise me that the NYTimes has a better rendition than CNN of how the jurors reached a verdict of guilty only on the manslaughter and not the murder. They report here that some jurors said that there was insufficient evidence of Killen's intent in setting this up.

Mr. DA mentions the possibility of misdemeanor manslaughter, before pointing out what has been sitting there in my mind the whole time - Jury Nullification (this is probably in the minds of many, but people are too afraid to raise the old specter of white southerner jury nullification in civil rights trials as being "unfair" to the south, and since the south does run the country these days, we can't be mean to them).

I just can't see what else it could be. Is there any doubt that there was a plan from the very start to kill these civil rights workers. Let's face it, evidence was presented that Killen gave instructions on where to bury, how to bury, to wear gloves, they used the local police to detain the people to put the plan in action, they killed them for no reason at all. I'm feeling pretty inadequate right now, I have trouble getting manslaughters on cases where one gang member shoots another gang member who previously beat up his homie, or where he went into a rival's territory, got shot at, and shot back and killed someone, or where a guy accused of stealing someone else's drugs gets attacked by 3 guys with guns and kills one of them. I got manslaughters on all of them, but it was like pulling teeth, and I had to go to trial first on 2 of them. But this takes things to a whole new level, if you can go and execute people and have a jury of your peers call it manslaughter, I need to do a better job of jury selection, I guess. My clients are right when they complain that they're not getting a jury of their peers when there are no fellow gangbangers on their panel.