This is a great game, my only complaint is that when you snipe an enemy unseen by bow, they run around for 10 seconds and then go back to their post. You hear them say, " Is someone there?" then, " I guess it wasn't anything".. Meanwhile, there is an arrow sticking out of their chest. I wish the AI would keep searching especially after being struck by an unseen foe. The same goes for when you drop one of the two guards, and the other guy walks past the dead body with no reaction. I wish this part of the game was better written.. That was my only complaint. Other than that, it is an incredible game. Beautiful scenery and breath-taking views.

Good job Bethesda.

For me, when enemy NPCs walk by a dead body they usually say something along the lines of, "I'm going to find out who did this!"

A bunch of dragons took out some NPCs in Riverrun. I dragged Alvar's corpse in front of his home. His wife walked by, said something like "what happened here" then went on her merry way. Same with his kid. *shrug* Maybe they just don't care if their family members die?

Bethesda, I am dissapoint.

In oblivion this issue was fixed with a one or two mods under a megabyte in size. Why was it not on a list of thing to improve?

Because they were too busy telling journalists how snow piles up on the terrain, and how the map is 3d.

Same thing happens to me. I've even had NPCs start a search upon finding a dead body.

Here's what I think happens:
The script takes a moment to kick in.
Second, if NPCs have performed one search of the area on finding a dead body and find nothing, they won't do it again. Why bother? They would assume the assailant has left the area.
For bandits and the like I also assume they aren't all that torn up on losing one of the gang. That's just a bigger cut for them.

For gameplay reasons it would make being a stealth character a lot more frustrating if forts and towns stayed on constant alert and search after finding a body, even if that would be more realistic.

This helps make it more believable, just imagine this is the case:

Bandits get shot in arrows by punk kids and annoying thugs all the time. When you do it, they look around for a while, but then give up. To the bandit, that's the 3rd time it's happened today.

As for bandits in caves, imagine the bandit think his arsehole bandit friend is effing around with him. "Hey who did that? Oh, dangit Jerry, was that you? Real mature, idiot. Get back to your post!"

Of course, then you pop out of the shadows with your knife around his neck, telling him "Jerry's dead" before you slit his throat.