Person B does not experience any such deprivation, however. Person B is dead the moment that Person A executed their murder and is blissfully unaware of the the entire activity throughout it's formulation, execution, and obviously it's aftermath.
So if a murder is painless for the unfortunate person murdered, it doesn't matter that their ability to experience anything is taken away?
Help me out here. My working summary of your argument is something like this:
1a. An action that has disadvantageous consequences for actors within societies is immoral.
1b. If an action x is committed by actor A upon actor B in society S, the consequences of x upon B and S are respectively dependent on B and S's perception of the consequences.
2. B is unable to perceive the consequences of x.
3. x does not result in perceptible (negative or positive) consequences for other members of S.
4. x has no disadvantaging consequences (2, 3).
5. x is not immoral (1a, 1b, 4).
I also am unaware of anyone advancing a right that people not be deprived of life arbitrarily, indeed our hostile environment would clearly belie any such right.
You appeared to state that rights existed, and so I've played along. Murder is conventionally considered a criminal offence, by which the public is wronged as well as the person murdered. Many might argue that this is a corollary of a right not to be arbitrarily deprived of life.
Thus as no right has been infringed upon, it would appear that you are instead condemning the nature of the action committed by Person A. At best then, you could call this a victimless crime, but that still does not clarify the morality of the action.
I haven't condemned anything. This whole scenario strikes me as a variant of the "if a tree falls in a forest.." thought experiment, where you're asking if it's immoral to commit an act where nobody is around to perceive an immorality; you've then pursued an apparently consequentialist line of argument, down to postulating that no subjective disutility incurs to anyone else, and that dead men are unable to perceive utility anyway.