Well, every time I go downstairs the smaller female fish that killed him is sitting in the cave that he used to chill in, so I can only assume it had to do with her wanting that portion of the tank for herself.
Sounds 100% accurate as far as what happened. Same issue with my JD when I had this territorial issue. Luckily I bought a separate 45g 4ft long tank and rehoused my JD before anything serious happened. He was really messing up the O though. Missing scales, split fins, etc.