Son Sen
Mam Nai was born in Kampong Thom Province in 1934, while Cambodia was under French domination. He was taught by Son Sen at the "Institut de Pédagogie" (Teacher Training College) in Phnom Penh, becoming a natural sciences teacher in 1956, and Kompong Thom's Balaign College principal in 1958. In the school environment he got to know Kang Kek Iew (Duch) who was his deputy principal. Both were arrested by Norodom Sihanouk's security services in 1967 owing to their leftist activities.