In the northern district of Anlong Veng, the final stronghold of the Khmer Rouge, a newly designed roof now shelters the modest tomb of Pol Pot, one of history’s most infamous figures.

But painful memories still endure of the murderous Khmer Rouge's time in power under the leadership of Pol Pot in the 1970s, when 2 million people – one-fourth of the population – died in the regime's ...