to preface, this is for a one-shot (to be reused in possible future campaign if i ever get the guts for it)

so, the basic premise is that i'm using the town of Hinderstap from the Wheel of Time:
a town where, at night, the inhabitants go into a murderous rage, killing everything, only to wake up unharmed, remembering it as just a bad dream in the morning, over and over.
so, the PCs are gonna get attacked by these guys, and then the next day see that anyone they killed comes back alive again.
(unless they just run away, which i have no idea how to stop)

and at the end, they're gonna find the source of this is a Wizard doing some fucked up Groundhog Day stuff, i'm thinking to keep a loved one from dying of an incurable disease, and the PCs can either fight him, or just convince him to stop.

anyway, i have the solution to the problem, but the issue i'm having is i have no idea how the PCs would actually figure it out.
i don't know how to give out the clues. any help would be appreciated.