I used to volunteer at my church (mostly to get out of sitting through service) which was a creepy building unto itself, 100+ years old, lots of creaks and unidentifiable noises constantly. Anyway, I was in the house part of the church, getting supplies from a closet when in walks the gardener, who always gave me the creeps as well. He just stood there by the door looking at me then said something along the lines of I shoudn't be creeping about by myself, I'll scare someone to death. I got out of there straight away with the excuse people were waiting for the stuff I was getting, the guy was just so weird, so unsettling.
A few months after that they found a body buried in the church grounds (had no graveyard) of this girl that had gone missing and guess who the killer was. Soon after that they linked the gardener to 3 other murders and suspected him of more.
TL;DR: was alone with a serial killer