One of the big things that made The Elder Scrolls Online feel so different from the previous single-player games of the series was the lack of any sort of justice system. NPCs were not killable, you couldn't steal from them and those things often made an Elder Scrolls game feel more fun. When planning for gameplay antics in TESO with a friend we were originally going to become a duo, she a vampire, me a werewolf, and we'd steal and assassinate our way across the map together. It was literally the first thing we thought of - killing all those we happened across.
Zenimax Online Studios covered implementing a justice system in their "Future of Elder Scrolls Online" panel at Quakecon, demonstrating how they see the system working in their MMO. To put it simply? They'll code in laws and NPC law officials, but leave it mostly up to players to decide how it works.
This means that you can choose to kill and steal from the NPCs, but you will gain bounties on your head similar to the single-player games. Capture by the NPC officials means paying a fine or fighting and fleeing for your life. Escape sin't the end of it though, as the bounty will remain which will make you a target for any bounty-hunter minded players out there looking to collect. As a system it could be a clever way to balance those who wish to commit crimes with those who would hunt them down; or it could need a little more control implemented to balance out either side.
I guess we'll find out which when Zenimax implement the new system into the game. Tell us how you think this'll turn out in the comments below!