People are understandably upset that the judge in the trial of Scott Roeder, who admits killing Dr. George Tiller, will allow the defense to put on evidence supporting a lesser charge of voluntary manslaughter rather than first-degree murder. The punishment for voluntary manslaughter is only a mandatory minimum of 5 years, while first-degree murder means life in prison.
I don't think it's going to work. Here's a good analysis of the hurdles such a defense would have to overcome to succeed. Roeder would have to prove that he had an honest and reasonable belief force was "necessary to defend ... a third person against such other's imminent use of unlawful force."
So, first, Roeder would have to show that he honestly believed there were reasonable grounds to think that Tiller's conduct was unlawful. I think that's almost impossible. The only argument I can imagine is that Tiller was accused in the past of performing abortions that violated Kansas law. Roeder could conceivably claim that he honestly believed Tiller had committed unlawful violence and would do so again, but I do not see the scenario where he shows that belief was reasonable. Tiller was acquitted of the charges in the past. And Roeder can't claim to know anything about the details of future procedures Tiller would perform, which I think you'd need to show to prove Roeder reasonably believed Tiller was about to break the law.
The imminence requirement is even worse for Roeder. Imminent means the unlawful action was about to happen at the moment the defendant used force to stop it. Roeder shot Tiller while he was handing out programs in the vestibule of his church. Even putting the best possible spin on this for Roeder, it would be the equivalent of spotting someone who you thought was a wanted murderer in the checkout line of the grocery store and, rather than call the police, shooting him in the back as he paid for his bread and milk instead.
The judge won't decide on whether to allow the jury to consider the lesser charge until after all the evidence is presented. My prediction is that the defense won't be able to present anything that overcomes these hurdles, especially the imminence requirement, and the judge won't include voluntary manslaughter in the charge.
In general, I think the judge allowing the defense to try to make the case is good on the level that all defendants should have the opportunity to defend themselves any way the evidence supports. But I think a conviction on voluntary manslaughter will be nearly impossible to obtain from an honest jury in the Tiller case. And if the jury is dishonest and inclined to sympathy for Roeder, it won't matter what charges are in the jury instruction, because they'd end up acquitting him anyway.