But concidering how this situation was described ... guard on one side of camp is killed, second guard on that same side of camp is bribed ... and then instantly whole camp knows that you are scumbag who allready killed one of their friends.
Kinda ruins the whole point of bribing, doesnt it?

It doesn't ruin the *whole* point of bribing, no. You still have gotten away with your crime at the cost of a bribe. Just in future you'll have to pay more or make a more difficult check. You can also think of it as: the guards know you will pay, so they'll try to extract more and more money from you, just as people do in real life.
As for your other points about realism/reasonable-ness, they're a bit hypocritical.
And money paid as bribes should be lost forever.
This is common practice in many video games and i honestly hate it ...
I allways wonder what did they do with that money? O_o
Did they eat, and allready digest it, so i cant get it back in any way?

Nah, sory but the fact that anything you give/pay/smuggle to npc inventory is still there for you to take after you kill them is in my honest opinion only good.
If you wish to have some "ensuring" mechanism ...
Those guards could yell at some other guards to acompany them on their way back to garrison, so you are discouraged to attack them in order to get that money back.
But you certainly should have that option.
You want one aspect of the system to be realistic (money not disappearing) but you like the fact that the other aspect is unrealistic - this exploit only works because a single guard/merchant "notices" any crime, even if their are countless other witnesses. In a "reasonable" world, the guard or merchant would shout "Stop! Thief!" while coming up to you, and everyone around you would hear this. And because people are nosy, they'd then watch you interact with the guard, put something in his hand, and then walk away. If the crime was murder, everyone would immediately know (or at least, there'd be rumors that) you're a murderer even if you successfully bribe the guard.
I would be fine with the suggestion in your last paragraph, where guards call for the others as reinforcements. But this would require that said guards *actually* are a force that could win against yours and that the money, once deposited in the garrison, it not trivial to immediately re-acquire. It also requires that every location have multiple guards and a garrison to do this. This is a bit too much realism to put in a game that is not centered around thieving.