Here is the full list of all 48 Heathen - there are The sons of the law achievements.
Kill crippleds
Discover this place
Kill flamers
Successfully learn stealth
Kill sergeants of the Faction 12
Find this item
Kill the heavy porter
Kill weird rats
Kill voices of the bats
Kill Facelesses sentinels
Kill porters
Kill sick porters
Complete the tutorial
Kill soldiers of the Faction 12
Kill heavy guards of the faction 12
Kill KERAS
Kill aquatic creatures
Kill lunatic rats
Kill shamans
Kill screamers
Kill armed guards upgraded
kill stinkys
Kill spearmans
Kill diggers
Explode smart moving mines
Destroy S.M.M Machines
Kill facelesses guards