Angel of Mercy (serial killer)
An angel of mercy or angel of death is a rare type of serial killer who is usually but not always female and employed as a caretaker. The angel of mercy is often in a position of power and decides the victim would be better off if they no longer suffered. This person then uses their knowledge to manufacture the death of the victim. As time goes on, this behavior escalates to encapsulate the healthy and the easily treated.
One theory to explain this particular type of serial killer is the Neutralization theory. Developed by sociologists Gresham Sykes and David Matza, it explains that criminals understand right from wrong. In order to neutralize their actions, criminals will develop new perceptions to mitigate the circumstances of their crimes. In this case, the killer might claim that he or she was helping the victim by easing their pain.