The other day I was traveling and decided to rest up in the Faregyl Inn. So I left my horse outside right next to the door. Inside a Khajiit asked me to find the thief who stole her jumbo potatoes. I accepted then immediately went outside to find the thief, so I went into the woods and killed the ogre who had stolen the potatoes. The ogre was not very far from the Inn so I wasn't gone long. When I returned my horse, who I just saw alive and well, was lying dead in the grass. I looked around but I saw no bandits, creatures nothing so I scouted the area around the Inn and still couldn't find a thing not even a rat. I have never had anything happen like this before and was wondering if anyone has ever had this experience and could help me figure out what happened. The horse is replaceable, but I'm still confused and very curious as to what happened.

I assume you've finished the main quest but oblivion gates always seemed to pop up around inns.

I had a very similar thing happen once, but I can't really provide any insight, since I know as little as you do. It was quite some time ago, so I don't remember precisely where it was or where I went, but it was the same thing - I came back and the horse was just dead. I searched everywhere around and found nothing at all - not just nothing that could've conceivably killed the horse, but nothing - not even a rat or a mudcrab.

I dunno....

You mean, Whodunit?

Must've been Lucien, Faregyl's right by the Inn of Ill Omen, maybe the horse was the next initiation target?

Lol yes this must be it I'm going with it.

Most wildlife creatures attack horses. I imagine one of them caught sight of your horse when you didn't notice, killed it, then returned to its normal patrolling location.

Oftentimes, if I'm going to venture away from my horse out in the wilderness, I tap my wait key first. That'll tell me if there are any hostiles nearby, since you cannot use the wait function if there are any.

I've found that running massive amounts of detect life is wonderfully helpful when traveling with or confirming a safe place for a horse. When outdoors, my character uses 360 feet.

Always remember, horses are in the faction called Prey Creatures, pretty much shows their place in the food chain, at the bottom next to deer and sheep.

I've had this happen to me several times. Usually, the horse will be left in some wilderness area, but I've also had this happen (horse dead, no apparent enemy nearby) in a safe spot, like (as you say) outside an inn.

Depends what level you are, I guess. A mountain lion or a bear for instance can travel far & fast.

Maybe someone got mad that your horse was parked in their way at the door. Put him in a proper parking spot next time.