What do you mean by "take a life"?
If you kill an Innocent or assist in killing, i.e. do damage to, an Innocent and they report you, it will add to the number of reports you have. Get too many and you are considered a murderer. There is no way for you to tell who reported you.

How will I know a murderer?
Murderers will be easy to spot. They and their name will be RED when your mouse pointer is over them. Further, "the Murderer" will appear after their name. (The floating neon sign, which was going to point to them, was left out… this time.)

How will I know if I become a murderer?
You will know because a system message will tell you that you have become a murderer.

How long will I remain a murderer?
You will be granted pardon for 1 murder for every eight hours of active game play. Should you commit a murder during this eight hours, your time will be reset. You will cease to be a murderer once the number of people you murdered is less than five.

What are the repercussions of being a murderer?
Here are the benefits that accompany the murderer package:

• Guards kill you on sight.
• A bounty is generated for the return of your head (sans your body.)
• Dying as a murderer causes substantial skill loss. (The amount of loss is based on the number of people you killed.) This skill loss is assessed upon resurrection.
• Vendors will charge you more for their services. (Being invulnerable makes them brave apparently.)