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 When showing the writs 1000 gold are withdrawn, the additional 40 gold you have to pay yourself or go to jail.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"Oblivion War Cry - New Dimension" where a bounty of 10,000 gold gets a one-hit kill, while showing the writs 1000 be withdrawn and the guards impose a death sentence against me.
Could one in the next version of the withdrawn bounty to over 1000 while showing the writs increase? Or search the entire bounty is withdrawn?