I totally underhand how you feel, I would be EXTREMELY upset if I even thought someone had hurt my horse. However, with no proof I would just be civil and kind to them, the only thing worse than a crazy neighbor is a crazy neighbor whose pissed off at you. If you start a fight now your only putting your horses in further danger because with no proof he will not be charged, but he will have nice new grudge against you. I'm not saying he did it because everyone is right, horses hurt themselves on EVERYTHING but in this case whether he did or didn't I would do some serious schmoozing in order to get on his good side. If he didn't do it, well then you'll just seem like a very nice person, if he did then maybe he'll start to like you and find someone elses farm to harass. I would also most definitely put up a few cameras, even if they are just game cameras because if he comes back, Then you'll have the proof you need to go after him.