An excellent piece. Important. should be more of this kind of exploration of the complexities involved before we rush to judgement.
The longer you study this period, the more you untangle the thousands of treads >> the less you tend to judge.

I can assure you this idea that the worst excesses of The KR were committed by a Vietnamese faction is alive and well today >> and not just in Anlong Veng.
Brother "No 2", Nuon Chea, (although increasingly recognised as the CKP/KR's real leader), forcefully prosecuted this case as the cornerstone of his defence at the KRTribunal.

It is also a view/line widely held by some of the more rabidly racist - but still significant in number and influence - members of the opposition. Educated people.
I actually think that this myth is growing in those circles - and their kids.

'Smart >> Utilising inherent Khmer anti Huon sentiment and amping it up to max by blaming Cambodia's greatest tragedy/failure on outsiders. - with secret hints and sneers at the ruling party's historical ties with, and support from, Vietnam.

I am no friend of VN, (and my wife has valid reason to hate them) but i reckon it is all entirely BS.. of course.
BUTT.. you better believe a minority but still sizeable portion of Cambodian society fully believe it. That is why the work of DC Cam and a whole bunch of other KR Tribunal-related initiatives are so important >> including the trials themselves - to set the historical record dead straight.

just my observations