Assassinations
From LSWiki
The Assassinations system is a dynamic, randomly-generated faculty of having an NPC tell you to go stab someone for rewards. It is generally intended as a replacement to other, more cumbersome methods of assassination tracking, such as those used by the Nizari. The syntax to use a particular assassination broker is visible in their OOC information listing (aka the info command).
Noteworthy Information
In some circumstances, you might be given an assignment to assassinate an NPC that cannot be killed (such as Malaclypse the Younger). If so, just abandon the obligation (type score to see the syntax) and get another one.
Often you will be tasked with killing useful NPCs such as trainers, bankers, and quest-givers, which may make some people angry. This is why you're being paid, so don't complain about it. If you can't take the heat, abandon the obligation.