It is a truism that the punishment should follow the crime. Thus, even if you know with enough certainty for court conviction that Smith will commit a crime, that is not enough for punishment.
But we need a qualifier. Punishment only needs to follow the crime in internal time. Smith builds a time machine while in prison and travels to 160 million BC. Now, there is a small police outpost in 160M BC, protecting time-traveling scientists from nefarious time travelers, and there is a small jail. It turns out that backwards time travel is much cheaper than forwards time travel (at any decent speed, measured in the ratio of external to internal time). To send Smith back to his time would be prohibitively expensive. There would be no injustice in jailing him in the year 160M BC, notwithstanding his protestations that he hasn't committed any crimes yet. For that's only true according to external time, since by his internal past, he had committed crimes.
Now, consider an apparent case of a person fissioning, say due to a Star Trek transporter malfunction. I used to argue that it is not tenable to suppose that the result of that is a single bilocated person on the grounds that it would be then be appropriate to punish the person in one location for what their copy in the other location did, which seems absurd. But I now think this argument is mistaken. For on the hypothesis that the person comes to be bilocated, we should now think of the person's internal time as having different branches corresponding to each location (this can best be seen by noting that we can run twin paradoxes between them). But then it is false that the person in location A can be justly punished at t2 for what the person in location B had done at an earlier time t1. For punishment should follow the crime in internal time. But since the two internal timelines are parallel, what B did is neither earlier than, nor simultaneous with, nor later than the punishment of A—there is no comparison between these internal times. Of course the external time of the punishment is later than the external time of the crime, but that is irrelevant. If parents took a 14-year-old Hitler for a time-travel excursion to our time, it would be wrong for us to now punish the young Hitler for the crime he had committed in the 1930s, since those crimes would not be earlier than the punishment in his internal time.
So while there might be objections to identity-after-fission, the punishment objection is not very strong.
One qualifier: It would not be wrong to set things up so that the punishment would be simultaneous with the crime, as long as the crime caused the punishment in the right way. So where I say that the punishment should follow the crime, I should include the possibility that the two are internally simultaneous, but with the crime explanatorily prior.