More recent media reports suggest a disturbing pattern of mutilation and murder. Last year, a mob in Papua New Guinea burned alive a young mother, Kepari Leniata, 20, who was suspected of sorcery. This highly publicized case followed a series of instances over recent years of lethal group violence against women and men accused of witchcraft.

“These are becoming all too common in certain parts of the country,” said the prime minister, Peter O’Neill. Last year, Papua New Guinea finally repealed a 1971 law that permitted attackers to cite intent to combat witchcraft as a legal defense. But progress is slow. Although the police charged a man and woman in connection with the 2013 killing of Ms. Leniata, no one has faced trial, a fact that drew protest from Amnesty International in February.

One of the ugliest aspects of these crimes is their brutality. Victims are often burned alive, as in Ms. Leniata’s case and a 2012 case in Nepal; or accused women are sometimes beaten to death, as occurred in the Colombian town of Santa Barbara in 2012; or the victims may be stoned or beheaded, as has been reported in Indonesia and sub-Saharan Africa.

It is tempting to point to poverty in the developing world, as well as scapegoating, as the chief causes of anti-witch attacks — and such forces are undoubtedly at work. But while Africa and the southwestern Pacific have a long history of economic misery, much of this violence, especially against children, has worsened since 2000. The surge suggests forces other than economic resentment or ancient superstition.