No motive??? Seriously?
I'm no FOX Crime detective, but how about...
1) British guy living large in a rural area in HKG.
2) Divorcee that just moved his 2 sons thousands of miles away from their mother.
3) "...running a training session..." Yeah, I'm sure everybody passes with flying colors.
4) He was a DO (DFO?). Who hasn't thought at one point in their lives that a rock would make a nice hat for a DFO?
There's always a motive!