A top South African court has declared that the country’s police and prosecutors are obliged to investigate allegations of torture and crimes against humanity committed by Zimbabwean government officials, against Zimbabweans, in Zimbabwe.

In a judgment handed down on Wednesday, the Supreme Court of Appeal said the South African law dealing with the implementation of the Rome Statute – the legal instrument which set up the International Criminal Court – required that the South African Police Service initiate an investigation.

The court said the police were empowered to investigate the alleged crimes “irrespective of whether or not the alleged perpetrators are present in South Africa”.

The case before the court arose from the refusal of South African authorities to investigate a case brought in 2008 by a civil society group and Zimbabwean exiles. The court said it believed the case was the first directly raising South Africa’s competence to investigate crimes against humanity.

A dossier handed to South African police and prosecutors in support of the case named a number of Zimbabwean officials as perpetrators of torture and implicated six government ministers in the alleged crimes.

Affidavits gave what the South African court called “a graphic picture” of torture allegedly carried out on members of the opposition Movement for Democratic Change after a raid on its offices in Harvest House, Harare: “They describe severe physical assaults being perpetrated, which included the use of truncheons, baseball bats, fan-belts and booted feet,” the court said. “There are accounts of victims being suspended by a metal rod between two tables; of being subjected to water boarding; and of electrical shocks being applied to the genitals of some of them.”

Early in its 39-page judgment, the Court of Appeal said the question at the heart of the case was: “What business is it of the South African authorities when torture on a widespread scale is alleged to have been committed by Zimbabweans against Zimbabweans in Zimbabwe?”

In effect the court decided that when South Africa signed the Rome Statute, and then passed domestic legislation enabling it to meet it obligations under the statute, it became responsible for investigating charges under the statute.

South African courts may not be able to try suspects unless they are present at their trial, but their absence from the country does not prevent police from investigating charges, the court found.

It noted during the course of its judgment that prosecutors were concerned at the impact of an investigation on South Africa’s relations with Zimbabwe.

“One of the considerations,” the court said, “was that the President of South Africa’s role as mediator between the opposition and ruling parties of Zimbabwe would be compromised.”

Under South African law, the government has only one more option before it is obliged to implement the Supreme Court of Appeal’s ruling: it can argue that the case should be finally decided by the Constitutional Court.