Add a subrule to Rule 2.1.1 (Occupations), called “Alchemical Studies”:-

The Alchemist is able to perform autopsies on villagers who have died. Through the careful application and slow observation of certain herbs and metals, it is possible to determine whether a corpse is that of a werewolf, or of a normal human.

The Alchemist may email the Mayor to announce that they are performing an autopsy on any number of dead villagers. The Mayor shall privately respond, revealing the nature of each such villager.

(This is an occupation that’s already held by someone, but if people don’t trust the current Alchemist, they can easily hold a meeting to replace him.)