Ok, bare with me. You are out wandering the deserts around Vegas. On the horizon you see some people. You sneak closer to determine if they are friend or foe. Upon inspection they turn out to be friendly (aka good). However, one of them seem to be carrying a very nice weapon. You have been wanting to get one of these from Gun Runners for some time, but simply cant afford it. You decide to kill him for it.

Depending on if the game thinks the person is good or bad you will be rewarded/punished with karma instantly.

So this sorta builds forther on the idea that karma really needs a rebalance in this game. it is assuming that someone will eventually fix the karma issues.

What if you were to kill that person and get away with it? Why wouldn't you? There are no witnesses around (none alive anyways).

My idea is that whenever you kill a member of a faction, you naturally leave shell casings behind (if you use melee you still have the murder weapon on you). Once a faction learns one of it's members have been killed they send someone to investigate. The investgators go CSI and using.. CSI awesome.. they have a xx% chance of learning who kiled the person(s) (who being you ) Ofc, depending on you being a thurhough killer or not, you may have picked up the evidence (casings, spent cells, shotgun hulls)

I'm not familiar with scripting, so i dont know how this could be implemented, but i imagine it would go somethign like this:

person is killed ->
check performed to determine if PC picked up casings -> (This will ofc not be instant, but say you use a timer or something to delay the script activation , oh.. 1-2 days?)
if not: check if killed npc was human and belonging to faction ->
if not: no worries.. end script
if true: run some probabllity thing that causes the PC to lose reputation with the faction (or become hostile) after X amount of time.

The idea is to simulate that killing someone when nobody is around or nobody is left to tell anyone about it.. does nto have imediate consequences.. it might not ever have consequences.

Anyways.. thats the start of my idea. I dont have anything close to the skills that would allow me to make something liek this, but im hoping some modder ses it and takes a liking to it

...they're going to identify killers via shell casings in a postapocalyptic wasteland? And you suggest karma should be dependent on whether anyone's watching? If it didn't, it wouldn't be Karma.
What would make sense would be to make faction relationship change based on whether or not there were witnesses- killing an NPC should perhaps start a 30-second timer, so you have that long to kill any nearby members of that faction or they radio your attack in.

You know it's slightly disturbing how many people there are on these forums that believe that if you aren't seen when you do something evil then you aren't evil. Is New Vegas marketed at serial killers or something?

But we all want good karma so we don't have to try in the game! Why even have bad karma at all? GET RID OF BAD KARMA AND HAVE EVERYTHING GIVE YOU GOOD KARMA SO YOU CAN BE A GOOD GUY ALL THE TIME EVERY DAY! (aka friendly)