If the person to executions does not one hit kill, you get a bounty of 40 Gold for the attack + 1000 for the murder = 1040 gold bounty. When showing the writs 1000 gold are withdrawn, the additional 40 gold you have to pay yourself or go to jail.
There is also a conflict with mods that increase the bounty for murder. I play for example with the Mod "Oblivion War Cry - New Dimension" where a bounty of 10,000 gold gets a one-hit kill, while showing the writs 1000 be withdrawn and the guards impose a death sentence against me.
Could one in the next version of the withdrawn bounty to over 1000 while showing the writs increase? Or search the entire bounty is withdrawn?
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Do you have the option to
Do you have the option to taunt the NPC via dialogue? Keep taunting them until they attack you and then it should be fine to kill them.
I know that the very first guy you have to kill has only one line of dialogue and then it exits, so you can't taunt him - everyone else should work though.