Suppose a man commits murder and is then promptly involved in a car crash that leads to complete loss of all his memories prior to the car crash. The police have indisputable proof that the man did indeed commit the murder. Should they prosecute? If you conclude that they should because in some sense he's physically the same person what if a murderer somehow makes a copy of themselves and then commits suicide, should the copy be prosecuted? If you conclude that they shouldn't be prosecuted because the person after the accident is a different person from before the accident what if there's indisputable evidence that all of their memories will return in 5 years? 5 weeks? 5 days? To my mind the person after the accident is a different person from the one who committed the murder and should therefore not be prosecuted. If the memories return then they should be prosecuted but we shouldn't punish them for a crime "they" didn't commit. But I am unsure as to how much of their memories need to return before they again become liable for their past actions.

Wow, you have come up with a case I love to use in my philosophy of mind to connect issues of personal identity to moral responsibility and "moral luck." I have students read the Oliver Sacks' case of Donald ("Murder" in The Man Who Mistook His Wife for a Hat). Donald took and, while high, killed his girlfriend. He had no memory of the incident (assume this is true for now) and was found not guilty by reason of (temporary) insanity. A few years later he was hit by a car and suddenly (re)remembered the gruesome murder (offering details only the killer could know). The case raises lots of questions: Is Donald on PCP (DPCP) the same person as Donald before (DBefore)? And is Donald at trial and the next few years (DTrial) the same as DPCP? And is Donald after recovering his memories from the accident (DAfter) the same as ... and DTrial and DBefore??

And beyond these questions about personal identity, there's the question of moral luck: assuming that Donald before (DBefore) had no more reason to think he'd become a killer than anyone else planning to take PCP, should DTrial (or DAfter) be charged with murder (DPCP seems to have intentionally killed his girlfriend, as in second-degree murder)? Or is Donald on PCP such a different person that it is only fair to blame him for doing something as stupid and illegal as taking PCP but not for murder?

So far, I've basically just re-iterated your very interesting questions, but I thought the parallels were interesting. Now, how to answer them? Well, everything depends on your theory of personal identity. If you hold John Locke's memory (or same consciousness) theory, as you seem to, then it seems that DTrial should not be punished for what DPCP did since he can't remember it, but as you suggest, DAfter could be punished for what DPCP did--unless you want to bring in the moral luck worry and say that even though DAfter remembers it, he shouldn't be blamed for more than taking PCP since DBefore had no reason to think he'd do what DPCP did! Except you might think there is something bad about DBefore's character that predisposed him to murder when he loses his inhibitions! Or you might want to charge him with manslaughter as we do with drunk drivers who kill (another case of moral luck since the drunk driver who doesn’t kill may have just gotten lucky someone didn’t cross his path). And then there's the (epistemic) problem of how we can know whether DTrial is faking it or not (the problem of other minds rears it's ugly head). Even Locke suggested that we must punish the man who commits a crime while drunk and says he doesn't remember it because we can't be sure, and we have to deter others from trying to get off by committing crimes while drunk (well, he said something like that). So, as a general rule we may need to punish bodies for what they do even if they claim not to remember doing it. Or we may decide to punish bodies because we hold a bodily criteria for personal identity. If I read Derek Parfit right, he seems to suggest that our practical interests (such as legal responsibility) will set the boundaries of the conditions for personal identity (e.g., we'll just have to stipulate what to say about weird cases) rather than there being a metaphysical truth about personal identity which we then apply to our practical interests (such as legal responsibility).

I better stop before I try to deal with your case of the murderer copying himself.

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