A man lay sprawled by the roadside in the Ukrainian city of Bucha on Sunday, his hands tied behind his back and a bullet wound to his head, one of hundreds of local residents that officials say have been found dead in the wake of five weeks of Russian occupation.

Bucha's deputy mayor, Taras Shapravskyi, said 50 of the dead residents, found after Russian forces withdrew from the city late last week, were the victims of extra-judicial killings carried out by Russian troops, and the officials have accused Moscow of war crimes...