Marshall Scott/Ethics

Hunting:

He likes to consider his victims parasites on society and that removing them is a public service. Being a cop for so many years means that he's still out there to protect people from the 'monsters' on the street - even if that means becoming one.

Killing:

Marshall only kills when he needs to feed. Since he hasn't quite got the hang of being able to take small amounts or to seduce his victims, he ends up killing them. The good news is that this means he's able to feed from them over several days. The bad news is that he's killed someone and has to deal with the body - and the psychological ramifications.