This form of serial killer is usually employed as a caregiver or medical professional and intentionally harms patients in their care.  Using their trained knowledge and expertise, these killers usually fit into the following 3 categories:

• Malignant hero: This is where the subject endangers the victim's life in some way and then proceeds to "save" them. Some feign attempting resuscitation, all the while knowing their victim is already dead and beyond help, but hope to be seen as selflessly making an effort
• Mercy killer: Believes the victims are suffering or beyond help, though this belief may be delusional. Also known as a angel of mercy.
• Sadistic: Use their position as a way of exerting power and control over helpless victims.

See our examples of angels of death below: