After I reported on the case of Donald Miller, the Ohio man who failed to convince a judge he should not be considered legally dead ("'No, You're Still Deceased,' Judge Tells Dead Man" (Oct. 10, 2013)), several people wrote in to ask what would happen if, for example, Miller was asked to pay taxes or charged with a crime. While the statute in question does say that a legal death is presumed to have occurred "for all purposes under the law of this state," my guess was that the state would not have much trouble ignoring such language in appropriate circumstances.
I was right.
Miller himself, to my knowledge, has not yet needed to assert a death-based immunity. The federal government has insisted that his daughters pay back the death benefits it paid them, even though their father is just as dead now as he was then, but at the moment that's still their problem. We might have an answer, though, to the criminal-defense question.
And the answer is that not only is death no defense, if you kill someone else while dead you can still get the death penalty.
According to several reports (FindLaw, Huffington Post), a Mississippi man who was declared legally dead in 1994 was sentenced to actual death last Friday for a kidnapping and murder he committed in 2010. While he was prosecuted under federal law, as far as I can tell the issue of his state-law legal status never came up. It doesn't look like it would have helped anyway, because the Mississippi statute is more limited than Ohio's, but I seriously doubt any court presented with this argument in this kind of case would get to the point of statutory construction. So, once again, I am shown to be master of the relatively obvious.
Further reading: Jeanne Louise Carriere, "The Rights of the Living Dead: Absent Persons in the Civil Law," 50 La. L. Rev. 901 (May 1990); see also Cecil Adams, "What happens when someone 'legally dead' shows up alive?" The Straight Dope (June 13, 2006).