The guy was a demented fruit loop -- who knows what "issues" he might have worked up in his sick little mind.
I'm betting it was something stupid, like he saw The Witness 20 years ago, saw some sweet-faced Amish girl he could fantasize as being like Kelly McGillis, and never got over the shame of being rejected.
I think I heard something today a little different. But along that line, I have heard that Amish teenagers are given a time in which they can do as they wish and then they are given the opportunity to come back to the group. Ibelieve I saw a documentary on this a few years back.