Is there a X-file episode where the investigation concluded "natural" cause?

I watched season 1 & 2 recently and in each episode the cause of whatever they were investigating was either outright or at least very likely to be of supernatural origin. The only episode that came close to a mundane conclusion was the one where they linked the murders to a feral human, a Sasquatch of a kind, living in the woods of New Jersey. I don't remember the other seasons very well, but I'm wondering if any episode concluded that the cause of the crime was due to "natural" causes?