Edit:
If someone doesn't see you kill someone the game shouldn't register as if you would have been seen slitting someones throat in town square. If I attempt to murder someone at night and they survive one hit I get bounty for assault. But If I kill her and nobody see's me I get a 1000 bounty. I've heard this is to cause they cry for help or something. But telling by the volume of their voices, c'mon really?
I think it should work similar to Red Dead Redemption's murder system, if you have a witness of the murder you can kill him or bribe him (Except Guards). But if he escapes you get a bounty, which is logical.
Remember Morrowinds dispose corpse option. If I am correct. You have to kill a woman in Chorrol(Dark Brotherhood), and she was talking to some other woman, I killed her. And the woman just staring into the air as if nothing happened when she just saw the woman she was talking to dead with an arrow in her head. Of course I got no bounty because it was a quest, but still. I kept playing on that save and everytime I went to Chorrol I would see her corpse still there. And people just passing by as if the corpse were invisible. If a citizen or guard see's a citizens corpse they should dispose of it or something...