Ooh, this is a legal question! Should Tyler be charged? Let's dive in...
To begin with, we don't really know very much about Federation law, or (more pertinently) Starfleet law, which is to say whatever futuristic permutation of the UCMJ may exist. All we can do is speculate based on current law. It's important to note, however, that civilian law
is different from law that applies to service members; the latter gives defendants fewer rights.
On the one hand, I can see why Tyler should be charged. Culber was murdered in cold blood, and it was clearly Tyler (at least his body) who did it. Of course at trial he'd be able to bring the defense that he wasn't in control of that body's actions, and whether this was true would be a question of fact for the court to determine. If he were acquitted on that basis it would presumably be some SF-nal analog of "not guilty by reason of insanity," so even if not technically guilty it would be important to determine whether any remnant of the Voq personality remained. If not he'd be a free man, but if so he'd presumably be detained for treatment until that determination could be made with assurance.
On the other hand, I can also see why Tyler should not be charged. In the real world the state (and the military) always has
prosecutorial discretion to avoid pressing charges in a case that's likely to lose, or in which winning wouldn't serve the interests of justice. In the Starfleet context, presumably Saru as the current commanding officer is in a position to determine how to exercise that discretion. It appears from the conversation we saw that he's inclined not to hold Tyler responsible for his actions, but doesn't trust him entirely (hence the detention bracelet). In a civilian context Tyler could probably argue "either charge me or let me go," but this is Starfleet, and UFP security issues are involved. While the conversation didn't frame things in legal terms, then, it would seem that Saru is still holding Tyler under (loose) detention, reserving the right to make a final decision about charges until he can determine whether any trace of Voq is still riding shotgun and trying to grab the steering wheel. It also makes sense to hold at least the
possibility of charges over Tyler's head at the moment, if only as an incentive to get him to plumb Voq's memories and share any relevant intel he might possess.
So that's the legal context. Above and beyond it, of course, there are ethical and philosophical questions...
Yes. ... But apparently Disco folks are OK with this and willing to pretend that this brainwashed murderous Klingon is actually the person in whose murder he participated in and whose skin he stole.
Voq has been brainwashed to think he is Ash Tyler. ... Original Tyler is dead. Voq is not the same person any more than a person suffering from delusion that they're Napoleon is the real Napoleon.
You seem to have strong opinions about this. In a real-world context (a Manchurian Candidate kind of situation), you'd probably be correct. But it's worth recognizing that despite much of what we know about how minds work in the real world, in the Star Trek universe Cartesian mind-body dualism is very much a thing. In story after story we've seen that one's consciousness is the real source of identity, regardless of what meat suit (or other container) it happens to occupy at the time.
In that context, if Tyler's personality was implanted in the (altered) body that once also housed Voq, and is now controlling that body... well, he is Tyler, and Tyler is him. He can't be held responsible for what Voq's mind did, regardless of what body it used at the time.
In Search for Spock? He was not a copy. He was rejuvenated original Spock suffering from amnesia.
How did you get that impression? The Spock in
STIII was clearly a new body grown from scratch, not one "rejuvenated" from the original. Spock's consciousness (minus a few memories) was subsequently implanted therein. From that point on, for all intents and purposes it was Spock. (More dualism at work.)