Regarding the matter of "himself" being killed, Aiden retained a memory, but this memory was extremely vague.
He only remembered that the person who killed "him" wore a mask of the Blood Moon Cult and pierced "his" heart with a gun during a fierce battle.
In that Blood Moon Cult which was destroyed by Silvertown's Inquisition of Heresy, either the core members of the cult committed suicide or were killed in desperate resistance, with the only exception being the mysterious founder who remained at large.
The previous owner of this body was a mighty person capable of capturing an S-class criminal single-handedly.
At least, as far as Aiden's impression went, the former owner of the body must have resisted; at the very least, he wasn't instantly deprived of the ability to resist during a sneak attack.
To defeat and kill such a senior Judge, the founder of the cult definitely had exceptional strength, without a doubt.