This quest is heavily bugged.

Usually players should find zombie Jack in the cave with Evelyn. If he's not there you just encountered a quest-breaking bug (murder quest + councillor's wife quest). And the hexagonal amulet needed for the crypt under the church is missing in many cases as well. This is another quest-breaking bug (undead invasion quest)...

You can at least end the undead invasion quest without the amulet by teleporting through the field in the crypt under the church. But there is no way to solve the murder case quest and the councillor's wife quest as far as I know...

I think I might even know why this bug happens. I've entered the church and the crypt before I've entered Evelyn's cave. And in that case zombie Jack appears in the crypt under the church and not in Evelyn's cave where he should appear first in order to proceed with the other quests. If you want to prevent the bug don't explore the church before exploring Evelyn's cave (or maybe I'm wrong, it's just my speculation).

WOOS