As I’m currently on 72 hours played non-lethal (0 killed humans and animals) except the commander who just had to get oneshotted with a bow, I wanted to make the bugged quest with crashes without unnecessary kills
Shortly:
Travel to Merhojed, speak to all except the old Straw (Sláma) - do not talk with him
Travel to the Sasau Monastery, make the cure
Travel back, talk to Nicodemus, talk to Melichar to open the “jail” for you
Cure the prisoner, wait 2 hours crouched behind him, knock him out (make unconscious from back), steal the letter
Go to Radzig with letter, save the game before talking with him or skip the second cinematic, it can crash as well
quest completed, the game considers prisoner dead but you do not have to kill him nor get a kill count
The whole quest guide below