Following on from the ideas about bounty hunters and a police force, you could combine the two ideas.

If someone comits a felony -  not necessarily murder, it could be theft, inuslting behaviour etc. too - their name could go onto the wanted list which other people have invisioned.

People could then either take up bounty hunting as a profession, or just simply a way as making quick money.

Bounty hunters would then attempt to track down the criminal; even perhaps if the criminal escapes capture for a certain amount of (logged in) time they get taken off the wanted list. But if the criminal gets cornered then the choice of options is determined by the alignment of the bounty hunter. For example a good bounty hunter would only accept the criminal going to jail, and an evil one would either be allowed to kill on the spot or take a bribe to say that they killed him/her.

However, for all alignments the criminal could get the option of attacking his/her bounty hunter instead. For example a lv10 wanted character would not attack a lv30 bounty hunter, but a lv40 one would. This would mean bounty hunters would go after criminals that are about the same level. With the disadvantage of a lower award for bringing in or killing lower leveled characters.

However I also like the zoned ideas, but I\'d prefer it if there was a reason for that area being safe, like magicback suggested.