The Lemurian Vampire 1st Case Achievement in The Case of the Golden Idol

You technically only need to find the clues required for the solution. Every clue in the game is marked with a ?/! and will turn into a check mark when you fully interact with them to find all the relevant details.

Solution:
Sutul Vaito went to the tower and said the incantation, because according to the local tradition, whenever the dweller endangers the community, the sentinel goes and banishes the dweller to the tower until the next time. After the incantation was spoken, the golden idol was activated to reduce lifespan and Sutul Vaito died.