Yeah he can't flat out murder of kill a candidate of his own power and being. He has to rather trick them, put them in a situation where people's true fears, faiths and nature come to surface, and because he believes every man's very nature is to sin and corrupt, he bases his plans and methods of elimination on the people to make it actually happen. Or he manipulates them in the form of people they know who have died, as we are fully aware of. The bastard.
And yeah, he's killed tons of people in his true form.