Has anybody been able to figure out what we're supposed to do with this? I've gotten the Nightkin to come and kill one of the brahmin, but then he just goes and stands behind a rock and talks to himself. He sits behind the rock indefinitely. Killing/pickpocketing him for the note doesn't do anything either, if you talk to the rancher afterward your only dialogue when asked about the cattle attacks is that you still haven't figured it out.

Is this quest just broken?

If it helps at all, I saw a machinima video on youtube where the Nightkin attacks the Brahmin. He pretty much just shoots the Nightkin straight away and gets the note. :shrug:

Yeah, I've killed the nightkin and taken the note. But when you go back inside and the rancher asks you if you've found anything, all you can say is "Not yet."

I killed the nightkin took the note, went in to talk to rancher, had a dialogue choice for " you will be having no more cattle attacks " and he gave me some caps.

This quest, and many other are glitched. The nightkin was just standing outside the pen. I walked up and punched him and boon killed him. Quest over.