Theory Jim Thompson was killed by communists plausible, but not new 

I passed through Betong in 1970 and there was still a lot of anti-communist fighting going on in that area at that time. Many villagers were being slaughtered under various pretexts. I remember seeing photos in a Bangkok newspaper of an entire village that had assisted me with fuel for my motorcycle being wiped out. Damn shame. 
car720
Interesting that the report suggests death at the hands of the Communist Party of Malaysia was a new theory. When I was in the Cameron Highlands in 1972, it was very much a theory then. It is still one of several theories, pending evidence. 
Cats4ever
Plausible explanation, but no body/grave/watch, etc? 
davehowden
ThaiVisa