Don't know if one exists, so I'll write a VERY quick one here, assuming from scratch

1. Create two new NPCS -- one your Victim, one your Quest Giver.
2. Place them in the world.
3. Open the Quest Menu.
4. Right-Click the list of Quests, and Select New
5. Name your Quest.
6. Check that it is set to run at the start of the game. Give it a priority (I use 90, personally)
7. Click the "Stages" tab, make 3 stages: 0, 10, 20 -- Give 10 the "Go here" text, and 20 the "It is done" text
8. Click the "Topics" tab.
9. Click the thin bar, and select "Add Topic"
10. Scroll to "GREETING". Click OK
11. Enter Topic Text, and use the bottom section to set "GetIsID [Target] == 1" to Target is your NPC
12. Create a new Script, something like:
ScriptName AssinationScriptBegin OnDeathSetStage [QuestID] 20End
13. Attach that to your Victim NPC
This would give you a VERY basic quest, where the PC is given a job and completes it-- the quest would complete as soon as the NPC dies, without the Player having to do anything else; however, doing it this way should give you an idea of the basics so you can experiment with exactly what you want

I'd suggest testing out with a new .esp, and if you have any questions, just ask