Whenever a soul is chained down something evil usually surface. In this case the worst evil has broken through and it’s loose, creating havoc wherever he goes. For too long he has been tied down. His lack of freedom has given birth to a demon that now controls every thought and action. Where his power comes from nobody knows, but it’s obviously dark in nature.
What used to keep him trapped in one place is now his weapon of choice. Every kill is a reenactment of his struggle to breathe freely. This entails tying up his victim in such a way that they can’t move. They have to feel what he felt. The suffocation and horror of not being in control, which ultimately sends them over the edge is the sign to strangle them with his chain.
The process is slow and deliberate. He wants to feel every last breath as it leaves the body, only to end the ceremony by crushing their necks, making sure they won’t return.