PHNOM PENH, Cambodia (AP) — The office of Cambodia’s most celebrated filmmaker is filled with books on the Khmer Rouge. On his desk, on the walls, in the filing cabinets and in every corner of Rithy Panh’s dimly lit office are memories of his country’s greatest tragedy. Probing the painful past started as a coping mechanism for Panh and evolved into a career. For the past two and a half decades, Panh has made movies that he considers his duty as a survivor, and his debt to the dead.