Police began the arrests on Thursday, bringing in two Cape Town men, including a former police officer whom Stefan Smit had hired to help with security.

A police spokesman said the police had also raided the home of a 54-year-old woman who escaped and became a fugitive, but they would not identify her.

On Monday, Zurenah Smit turned herself in at the Stellenbosch police station, officials said, and she was confirmed as the third person to be charged with murder in connection with Smit's death.

In text messages with a reporter for The New York Times, Zurenah Smit claimed she was the victim of "conspiracies" and said, without producing evidence, that she had received multiple death threats. She would not respond to questions about being considered a suspect in the case.

According to local news reports, Zurenah Smit was present on the night of the shooting, when four men entered the farmhouse through an unlocked door and fired several times at her husband.

A bodyguard hired by Stefan Smit, Bradley van Eyslend, was in an adjoining room but later told investigators that he hadn't heard any gunshots.

Van Eyslend was not one of the men charged, officials said. But his half-brother, Derek Sait, who was also part of Smit's security team, was one of the two men arrested on Thursday.

Stefan Smit was known to be extremely vigilant about security, and the unlocked door struck people who knew him as suspicious, said Julian Jansen, a journalist who has covered the case.

Smit's electric perimeter fence showed no signs of forced entry, and video footage showed no attackers arriving or leaving.

Yet in a country where farm killings have become a divisive and combustible issue, Smit's killing immediately made headlines. Provincial authorities pledged to establish a new farm safety program, calling Smit's death "an attack on the economy".

On Fox News, Tucker Carlson devoted a segment to what he called "racist violence as brutal and indefensible as anything that happened under apartheid".

While there are cases of white farmers being murdered in South Africa, sometimes brutally, there is no indication this stands out from the nation's generally high levels of violent crime, according to researchers and fact-checking groups.

Nechama Brodie, a researcher who studies violence in South Africa, said that farm killings were typically associated with criminal violence, not politically motivated attacks on white farmers.

In Smit's case, media coverage is starting to focus on an apparent dispute between his family and Zurenah Smit.

Several months before his death, local news media reported, he had removed Zurenah Smit from his will, excluding her from an estate worth at least $US7 million ($9.3 million).

Included in that figure was about $US3 million from selling the occupied portion of his farm, Louiesenhof Wines, to the local municipality.

But after he was shot, Zurenah Smit produced a different will proclaiming her to be the executor of the estate. She claimed that she had found the document folded inside a Bible.

In recent court filings, one of Stefan Smit's daughters, Martine Smit, submitted a forensic report by a police handwriting expert claiming that her father's signature on that document had been forged.

A quarter of a century after the end of apartheid, white South Africans, who make up about 8 per cent of the population, still dominate the economy and own the country’s most productive land.

Smit's was the second farm killing in the Western Cape province in less than a month, said Jeanne Boshoff, a spokeswoman for a farming association, Agri Wes-Cape.

In a statement addressed to President Cyril Ramaphosa shortly after, the group asked why farmers should remain in South Africa if their safety, as well as that of their workers, could not be guaranteed.

In December 2017, the long-governing African National Congress, or ANC, endorsed the expropriation of land without compensation, although the policy is yet to become law.

Ramaphosa, who supports the policy, has tried to reassure anxious farmers, business groups and foreign investors that it would be carried out without the kind of violent land seizures that occurred in neighbouring Zimbabwe almost two decades ago, a policy that devastated its economy.

Smit's daughters and first wife declined to comment on the case for this article.

The New York Times