The historian Paul Johnson asserted that Sartre's ideas had inspired the Khmer Rouge leadership: "The events in Cambodia in the 1970s, in which between one-fifth and one-third of the nation was starved to death or murdered, were entirely the work of a group of intellectuals, who were for the most part pupils and admirers of Jean-Paul Sartre – 'Sartre's Children' as I call them."
How much truth is to this statement?
Is this a fringe idea or something that is commonly accepted?
What can we conclusively say about the ideology of the Khmer Rouge leadership?
I don't think there are many historians that would place an overwhelming value on the notion that the primary members of the Communist Party of Kampuchea were 'pupils and admirers' of Sartre. I think what Johnson might be getting at is the idea of the students who studied in Paris, (Saloth Sar, Ieng Sary, Khieu Samphan, Son Sen, Ieng Thirith etc) those who eventually formed a large part of the 'Standing Committee' of Democratic Kampuchea, were influenced by their time there. Paris in the early 1950s, in certain circles, was a very leftist/socialist environment. The French Communist Party was one of the most Stalinist in the world. I'm sure that Sartre's influence was part of the rich tapestry that they were absorbing, but I wouldn't be overstating his particular part of it.
As for what 'we can conclusively say' about KR ideology, it depends on who you ask. What I think any good answer to that question should include however is that it was not just one thing or another. It was a movement with nationalistic aims, with influence from the particulars of Cambodian nationalism, it was Marxist, Leninist, Maoist, Stalinist... it was influenced by Vietnamese communism, by the French revolution, it had Theravada Buddhist elements.
I've answered some other questions that get at the ideology of the KR, I hope they might also be useful: