Return to the Marshall Courthouse for this last mission of this series. Simply kill enough zombies until the mission is finished. This part is infamous for some glitching because some zombies gets stuck inside walls not allowing you to hit them at all, thus failing the requirement. To mend this problem, bring any firearm and hope for the best that a stuck zombie will stick its head out of the glitched wall, don't miss this opportunity to shoot its head and kill it.