I’m having a hard time understanding the why behind a transplant like this. It wouldn’t save the life of the person in the host body (in this case, the woman). Because the sense of self is contained within the brain, it would only be saving the life of the person who owns the brain (in this case, the criminal man). So, who is behind saving the life of a criminally insane serial killer by giving him the body of a now deceased (brain dead) woman? Who would want to do that? I’m curious about the motive behind that.
But I suppose that is only indirectly related to your question. If it were possible to do a brain transplant, I don’t think it would be done in this manner, so it wouldn’t line up with the story, no. Because, again, the brain is what contains the sense of self, and arguably, the “soul” or life of a person is tied to the brain because of that. So, if scientists or brain surgeons were to perform a brain transplant, it would be to save the life of the person who donated the brain, not the life of whoever’s body the brain was going into.
There’s a whole lot of various ethical concerns about using a brain dead person’s body that is only alive through life support to house another person’s functional brain as well, because those are both two separate people, or were before the transplant, and while you may be saving one life by doing so, you would also be causing immense trauma and lowering the quality of life for that person, while taking advantage of the dead to do so. That’s a whole mess that, as listed above, would require some incredibly interesting, if unlikely motives to make someone go through with doing the surgery at all.
It would make more sense to clone or genetically engineer a body for the brain, that is more compatible with it and won’t be violating human rights (at least not as much) to do so - or even use a robot and somehow hook the brain up to control it like a mech suit - than it would to transplant one person’s brain into the body of another person’s. Logistically, it just doesn’t make sense to me, unless it was some mad scientist’s experiment and they had something personal invested in such a procedure. Perhaps they were a relative of the criminally insane serial killer man’s and thought he was wrongly sentenced to death (I assume that’s how the brain was donated)? Then, out of desperation, they may use a readily available body of someone recently deceased, if the body was in good condition. It may be cheaper, but it would also be a crime to do so, so they would indeed have to be desperate.
That’s just an idea though. But it’s the only one I can think of that might make sense in this situation. Otherwise, it seems like a bit of a stretch logistically. The person performing the surgery would have to be, at the very least, morally unsound, if not mentally unsound as well.
It’s a very interesting concept, but one that requires a lot more in depth thought in order for you to spin a story around it that is capable of suspending disbelief in the reader.