+1 They should get in an alarmed stated and increase in number around the area for a short time, making it very hard for you to murder some more people in that short time. I would also like for Skyrim to have you dump your bloody sword so guards do not suspect you, or at least sleep somewhere hidden until the blood wears off before entering a city. But I think that won't be easy to imply, requires some serious AI.
Yeah the alarmed state and increased guard numbers would be a good touch, like guards running around asif there looking for someone,. Your second idea would also be good but i cant see it appearing in skyrim.