Here’s how the legal system – well, the Empire’s legal system, anyway – copes with forking. You are liable for all the crimes committed by you, or by the lineal fork-ancestors from which you descend. So if you commit the crime first, and then fork, both of you are liable. But if you fork, and then the other you commits the crime, you’re not liable, because you had neither mens rea nor actus reus. See?
(And, obvs., if you merge, you’re liable for whatever your constituents did, pre-merge.)
Unless you decided to commit the crime before you forked, and only one of you actually did it, because then both of you had mens rea. In which case, the one of you who did it will be prosecuted for committing the crime, and the other one of you will be prosecuted for conspiring to commit the crime – with yourself, sure, but conspiracy is conspiracy. And conveniently enough, under Imperial law, the penalty for conspiring to commit a crime is almost always identical to the penalty for actually committing it.
This applies even if you, the fork that didn’t commit the crime, don’t remember conspiring to commit the crime, because your progenitor redacted it out of your mind-state. Whether you remember it or not, you’re still the person that decided to commit the crime, which means you still had mens rea, even if you don’t remember having had it.
Unless, that is, the redactions and other mental editing done to you are sufficiently large to render you a different individual, for legal purposes, because that’s legally equivalent to killing yourself and creating someone new, and you can’t be held liable for the crimes of your creator any more than you can be held liable for the crimes of your parents.
And then there’s what happens if you decide to commit a bank robbery, say, and then fork, and then the fork that commits the crime has his plan go south and kills someone in the course of the robbery, in which case that fork can be prosecuted for corpicide or cognicide, as relevant, but the other fork of you can only be prosecuted for conspiracy to commit the robbery, since mens rea for that existed before the split, but that for the murder did not.
Now, about those three-fork cases…