A tourist visits the Tuol Sleng Genocide Museum, also known as the notorious security prison S-21, in Phnom Penh March 3, 2015. A U.N.-backed war crimes tribunal in Cambodia on Tuesday charged two former cadres of the Khmer Rouge regime with crimes against humanity over their alleged roles in the deaths of an estimated 1.8 million people in the 1970s. The tribunal, which has delivered verdicts against only three former Khmer Rouge since it was set up almost a decade ago, announced in a statement that Im Cheam and Meas Muth would be face trial accused of committing murder, slavery and political and ethnic persecution as well as "other inhumane acts." REUTERS/Samrang Pring (CAMBODIA - Tags: CRIME LAW SOCIETY POLITICS)