Senior police detective Frans Mathipa had been fighting for four months to gain access to a crucial piece of information in the case he was working on. Finally, he was told, it was going to come his way. But he feared his pursuit of it could cost him his life. Two days later, his car was found overturned - he had been shot dead while driving. This was reported by Qazaqyia.kz citing BBC News.

Now seven members of South Africa's special forces, and one military police officer, have been charged with murdering Lt Col Mathipa, a highly respected officer, in August 2023. They deny the charges. There has been no date scheduled for their trial, and there are concerns it will never go ahead, because three of the men charged with his murder have refused to comply with a court order revoking their bail. They are still working for the army's special forces, and one of them has been promoted.

The BBC World Service has been given exclusive access to the prosecution case against all the men. The case has caused consternation in one of Africa's most robust democracies, with fears the country's military is significantly overreaching its mandate. We asked the South African army whether it was responsible for Mathipa's killing. It did not respond.

Several hundred pages of secret police and court documents, shared with the BBC, set out the evidence suggesting special forces killed Mathipa - who worked for an elite police unit known as "The Hawks". We have also interviewed key sources in the police investigation - South Africa's former head of counter-terrorism in The Hawks; Mathipa's commanding officer; and Mathipa's family - to build the most comprehensive public account of the events leading up to the detective's death. It presents a compelling case that South Africa's special forces are responsible for his murder.

In particular, police documents show that the vehicle that trailed Mathipa just before he was shot was registered to a front company for the special forces. And that tracking data found in that vehicle puts it at the scene of the shooting. One of the men in the car, Maj Sunnybooi Wambi, the documents show, was also spotted at the scene of an alleged abduction carried out by special forces soldiers - the case that Mathipa had been investigating. After Mathipa's death, special forces issued a chilling warning to The Hawks, the police documents say. "You can appoint 10 investigating officers; we will kill all of them," said the warning, according to police.

The case Mathipa had been investigating was sensitive. It centred on an Ethiopian man called Abdella Abadigga, an alleged so-called Islamic State [IS] militant. He had been granted temporary asylum in South Africa in 2008, but was arrested abroad in 2017. Abadigga had then been smuggled back into the country, by the South African military and Department of Home Affairs, to be used as an intelligence asset - but had "gone rogue", according to Col Tollie Vreugdenburg, former head of counter-terrorism in The Hawks. Abadigga had gone on to extort Johannesburg's Ethiopian neighbourhood, sources in the community told us. This money was used to fund IS, says the US government.

We asked the South African army if it had facilitated Abadigga's return to South Africa. And we asked the Department of Home Affairs if it had lied about a planned deportation of him to Ethiopia, and had instead smuggled him back into South Africa on an expired passport and refugee permit. They did not respond. Specifically, Mathipa was investigating the allegation that special forces had then gone on to abduct and kill Abadigga in December 2022 - who the United States, earlier that year, had put under sanctions, designating him an IS recruiter and fundraiser, as well as a trusted supporter of Bilal al-Sudani, a top IS figure in Somalia.

Court documents show that after Abadigga's abduction, his phone connected to a mast near a military base. Police sources say it was used to call a number in Somalia. The Pentagon did not respond to the BBC's question on whether Abadigga's phone helped locate al-Sudani, who was killed by US special forces in Somalia in January 2023, only a few weeks after Abadigga's alleged abduction. We also asked South Africa's President Cyril Ramaphosa whether Abadigga had been kidnapped at the behest of the US. He declined to comment. When Mathipa was assigned the case, four months before his own death, he already knew special forces were implicated, but he was trying to secure more evidence.