Peter Godwin is the president of the PEN American Center and author, most recently of “The Fear: Robert Mugabe and the Martyrdom of Zimbabwe.”

For the past decade, South Africa has been the preferred vacation spot, shopping destination and international transit hub for members of the tyrannical and murderous government ruling its northern neighbor, Zimbabwe — a government that has rigged elections, beaten and killed opposition activists and ruined a once thriving economy. All of this could now change because of a landmark legal decision.

Last week, the High Court in Pretoria, South Africa’s administrative capital, handed down a historic judgment. It ordered South African authorities to investigate and prosecute members of Robert Mugabe’s government who had tortured their political opponents. Under South African law, the police are obliged to investigate evidence of a crime against humanity, wherever it occurs, if the rule of law does not exist there, as is the case in Zimbabwe.

The ruling has profound implications. It could cement South Africa’s commitment to protecting human rights and broaden the application of universal jurisdiction, which is the ability of countries to prosecute people who committed certain egregious crimes outside its borders. Unfortunately, the South African authorities want to sidestep it and are reportedly preparing an appeal to the Supreme Court of Appeal, which oversees the High Courts....