DIEPSLOOT, South Africa  The two robbery suspects had already been viciously beaten, their swollen faces stained with rivulets of red. One of them could no longer sit up, and only the need to moan seemed to revive him into consciousness. The other, Moses Tjiwa, occasionally stared into the taunting crowd and muttered, “I didn’t do anything.”

The suspects were awaiting the final cathartic wrath of the mob, the torment of being burned alive, wrapped in the fatal shawl of a gasoline-soaked blanket. Then suddenly they were saved from that hideous death by the brave intervention of a local politician. “Let the police handle this,” he implored.

As usual, the police arrived late on that recent evening, and many in the mob angrily objected to their being there at all. Finally, one police inspector shouted: “Get back or I’m leaving this place and never helping you people again. I hate Diepsloot!”

Crime in South Africa is commonly portrayed as an onslaught against the wealthy, but it is the poor who are most vulnerable: poor people conveniently accessible to poor criminals. Diepsloot, an impoverished settlement on the northern edge of Johannesburg, has an estimated population of 150,000, and the closest police station is 10 miles away.