President Nelson Mandela is caught in a verbal salvo in on-going controversy over the 1988 murder of a teenage activist Stompie Sepei, one of four young males who were kidnapped at the behest of Mr Mandela's ex-wife Ms Winnie Madikizela-Mandela, Patrick Laurence reports.Mr Mandela is all but accused of organising the abduction from South Africa and the imprisonment in Zambia of Katiza Cebekhulu, a young Zulu man who was originally indicted with Ms Madikizela-Mandela in the trial which led to her conviction for kidnapping in May 1991.In a new book released in South Africa yesterday, Katiza's Journey, Mr Cebekhulu implicates Ms Madikizela-Mandela directly in the slaying of Sepei, saying that while the teenager was held down he saw "her lift her hand and stab him twice".The book, by a British journalist, Fred Bridgland, quotes the former Zambian president, Mr Kenneth Kaunda, as saying that he was approached by Mr Oliver Tambo, then still the ANC's president, on behalf of Mr Mandela to give Mr Cebekhulu "safe haven".Mr Cebekhulu disappeared shortly after the start of the trial, only to resurface in a Zambian prison, where he remained until he was rescued by the former British MP, Ms Emma Nicholson. As the book makes clear, Mr Cebekhulu's disappearance related to fears that he might become a state witness and give evidence against her.Mr Mandela's office unequivocally denies that he had any hand in the disappearance or subsequent imprisonment in Zambia. Mr Cebekhulu makes several startling allegations which reinforce suspicions that Ms Madikizela-Mandela's involvement the "reign of terror" conducted by bodyguards goes beyond her conviction for kidnapping, allegations that Mrs Mandela vehemently denies.