The agent who performed an act of kamma and the person experiencing the result: the same person, someone else, both or neither?

"In his effort to master kamma in such a way as to bring kamma to an end, the Buddha discovered that he had to abandon the contexts of personal narrative and cosmology in which the issue of kamma first presented itself. Both these forms of understanding deal in categories of being and non-being, self and others, but the Buddha found that it was impossible to bring kamma to an end if one thought in such terms. For example, narrative and cosmological modes of thinking would lead one to ask whether the agent who performed an act of kamma was the same as the person experiencing the result, someone else, both, or neither. If one answered that it was the same person, then the person experiencing the result would have to identify not only with the actor, but also with the mode of action, and thus would not be able to gain release from it. If one answered that it was another person, both oneself and another, or neither, then the person experiencing the result would see no need to heighten the skill or understanding of his/her own kamma in the present, for the experience of pleasure and pain was not his or her own full responsibility. In either case, the development of the fourth type of kamma would be aborted [SN12:67, Ud6:6].

To avoid the drawbacks of the narrative and cosmological mind-sets, the Buddha pursued an entirely different tack — what he called “entry into emptiness,” and what modern philosophy calls radical phenomenology: a focus on the events of present consciousness, in and of themselves, without reference to questions of whether there are any entities underlying those events. In the Buddha’s case, he focused simply on the process of kammic cause and result as it played itself out in the immediate present, in the process of developing the skillfulness of the mind, without reference to who or what lay behind those processes. On the most basic level of this mode of awareness, there was no sense even of “existence” or “non-existence” [SN12:15], but simply the events of stress, its origination, its cessation, and the path to its cessation, arising and passing away. Through this mode he was able to pursue the fourth type of kamma to its end, at the same time gaining heightened insight into the nature of action itself and its many implications, including questions of rebirth, the relationship of mental to physical events, and the way kamma constructs all experience of the cosmos."

~ Thanissaro Bhikkhu "The Wings to Awakening"