Philadelphia has imposed a city-wide curfew starting Wednesday at 9 p.m. to try to prevent a third night of looting and violence amid widespread protests over the police killing of a Black man.Tension has gripped the streets of Philadelphia since Monday’s deadly police shooting of Walter Wallace, 27, who was armed with a knife and described by relatives as suffering from a mental breakdown, in a confrontation with law enforcement.

Philadelphia has imposed a city-wide curfew starting Wednesday at 9 p.m. to try to prevent a third night of looting…