A living puthujjana actually and in truth is to be found but not an arahant.
It sounds to me as though you think that an in the case of an unenlightened person there is some "actual in truth" soul / person / being, but not for an arahant. Do you think that becoming an arahant entails the destruction of this "actual in truth" soul / person / being?
Whereas "actual in truth" even a puthujjana is not to be found. That is what is meant by "not self", etc.
The difference between the puthujjana and the arahanat is not viz whether or not "actual in truth" there is a being to be found, but whether or not the defilements are present. Between a puthujjana and a sotapanna, the difference is whether or not the "identity view" is present.
It seems to me that you are conflating "actual in truth being" with "identity view". Whether or not some so-called being has an identity view or defilements is irrelevant to whether or not the term "killing" is applicable.
Although if an arahant were killed, they would not think "I (actually and truly) am being killed", this is irrelevant to the act of "killing". If the killer did not think that the arahant were "actually and truly" a living being, then they wouldn't have the intention to kill the arahant in the first place. Because such a person would be at least a sotapanna, thus incapable of committing any act which would lead to hellish rebirth, and thus incapable of killing an arahant.