In July 1990, five months after the South African government had unbanned the ANC, security police in Durban raided a local house. An informer had tipped them off about a group of externally trained ANC cadres giving military training to township militants. The way in which one breakthrough now led quickly to another gave police no reason to believe they were dealing with anything out of the ordinary - except perhaps that this training was taking place six months into what was supposed to be a new era of negotiation. But police were astonished at what they stumbled upon.

Their initial prize was Siphiwe Nyanda, the ANC's most successful regional military commander. Under the nom de guerre of Gebuza, Nyanda had headed the Transvaal urban machinery of the ANC's military wing, Umkhonto we Sizwe (or MK), since 1977. Based mainly in Swaziland, he had sometimes crossed into South Africa on operations. The last that South African intelligence, or most of his ANC comrades, had heard of him - in 1988 - was that he had been sent to the Soviet Union for an advanced military training course. They guessed the move was to prepare him for a senior post in the defence force of a putative post-apartheid South Africa.

The police haul of documentation indicated a worrying degree of ANC penetration of South African intelligence, the existence of an incipient national underground leadership of the ANC, as well as there having been regular three-way communication between Nelson Mandela in his cell at Pollsmoor Prison and the ANC leadership abroad, via this underground leadership; between the latter two, this communication had sometimes been daily. And it was clear that Nyanda and his associates had control over a large network of arms caches.

Another discovery followed: that the commander of this internal underground leadership was Mac Maharaj, a member of the ANC's national executive committee, one of Mandela's closer colleagues in Robben Island prison between 1964 and 1976, between 1978 and 1983 the head in exile of the ANC's internal reconstruction and development department and, since then, a leading member of the ANC's main operational organ, the Politico-Military Council. Maharaj, police found, had lived underground inside South Africa since July 1988 - for some 18 months before the ban on the ANC had been lifted. Before his disappearance from the ranks of ANC exiles in 1988, ANC members had heard Maharaj was desperately ill with a kidney complaint in the Soviet Union.

Police also discovered that Maharaj and Nyanda had been joined inside the country by Ronnie Kasrils in early 1990, a few weeks before the ANC's unbanning. Kasrils, also a member of the ANC national executive, had headed ANC military intelligence between 1983 and 1988 and, after that, had served as secretary of the ANC's internal political committee. Shortly before his disappearance from the ranks of exiles, ANC colleagues heard he had been seriously injured in a Jeep accident in Vietnam.

Moreover, police investigations revealed that, after the unbanning of the ANC on February 2 1990, Nyanda had remained in place underground inside the country, while Maharaj and Kasrils had, in order to preserve the security of their project, clandestinely left the country, returning to it openly by a circuitous route.

In July 1990, in the midst of delicate opening moments in the new era of negotiations, security police arrested first Nyanda, then Maharaj, followed by a number of other key figures in the operation. Kasrils went underground again.

From: Conscripts to their age: African National Congress operational strategy, 1976-1986 by Howard Barrell