PHNOM PENH, June 27 (bdnews24.com/Reuters) - The four  most senior surviving members of Cambodia's murderous Khmer Rouge regime went on trial for war crimes on Monday, three decades after its "year zero" revolution marked one of the darkest chapters of the 20th century.  The defendants, all now elderly and infirm, were among the inner circle of the late Pol Pot, the French-educated architect of the Khmer Rouge's ultra-Maoist "Killing Fields" revolution that killed an estimated 1.7 million Cambodians from 1975-1979.  Dressed in casual clothes,  "Brother Number Two" Nuon Chea, former President Khieu …