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Macaca fascicularis
Spotted on the road to Angkor Wat, where this monkey is clearly accustomed to getting freebees. I could not find any information online to identify the exact species.
This is actually a macaque and most likely the crab-eating macaque. There is a bit of a contradiction in your notes. You are right that the genus Ateles and family Atelidae is a New World group of monkeys, unfortunately, Cambodia is considered Old World. The New World is North and South America and surroundings.