You have agreed to do some chores for Captain Álarr in exchange for access to the murder location. Clean up the filthy guards' barracks.
'You know what I really need around here? Someone to clean this mess! My guards are filthy, despite how many times I've scolded them for it! How hard is it to wipe your boots off before you come inside? Do me a favour and clean up after them.'
Mud can be found in the guards' barracks in Lake-town.
You should clean up mud.
Captain Álarr can be found in the guards' barracks in Lake-town.
You should talk to Álarr.