Cyril Zakele Mbatha, serving a life sentence for Dr Asvat's murder, said in his submission: "I killed Dr Asvat by shooting him with a 9mm gun.
"This was under instructions from Mrs Mandela and I genuinely believed that I would be benefiting the future political system of our country."
News of the confession by Mbatha, who is scheduled to appear before the Truth and Reconciliation Committee tomorrow, is certain to cause a furore when the Commission reconvenes today under the chairmanship of Archbishop Desmond Tutu.
Mbatha said he was initially given a gun by his accomplice, Nicholas Thulani Dlamini, to assassinate Asvat on 27 January 1989. The gun jammed, so they were taken by car to Mrs Mandela's Soweto home. "This was for the purpose of changing guns," said Mbatha. Dlamini and the driver waited outside. "Mrs Mandela said if we killed Dr Asvat we would be paid 20,000 rand [pounds 4,000 in 1989] ... [and] we would be doing it for the cause of our country." Mbatha said Mrs Mandela ordered Katiza Cebekhulu - the so- called "missing witness" in the Winnie Mandela saga - to guide them to Asvat's surgery.
An appointment had been made with the doctor. Dlamini sat in the waiting- room with Dr Asvat's receptionist, Albertina Sisulu, wife of ANC chief, Walter Sisulu.
"I went into Dr Asvat's rooms and I shot him twice in the chest," said Mbatha. "Dlamini panicked and tried to climb out of the window, but I shouted to Mrs Sisulu that if she did not open the security doors I would kill her ... I ran out, together with Dlamini."
The South African Police have been accused of covering up the full facts about the Asvat murder, which happened four weeks after the killing of Stompie Moeketsi.
Evidence has emerged at the TRC hearings that Dr Asvat examined Stompie at Mrs Mandela's house after he had been severely beaten, on 29 December 1988, by her Mandela United Football Club. Asvat told Mrs Mandela that Stompie was so severely injured he would die unless taken to hospital. Stompie was stabbed to death later that night. Katiza Cebekhulu earlier this week accused Mrs Mandela before the TRC of personally killing Stompie.
Asvat was also asked by Mrs Mandela to provide a certificate saying Cebekhulu had been sodomised by a white Methodist minister, Paul Verryn. Asvat refused because there was no physical evidence of homosexual rape.
The Asvat family has long believed the motive for Abu-Baker's murder was not robbery, as police stated at the time. It is, however, known that Dlamini made a statement in 1989 saying Mrs Mandela had offered him money to kill Dr Asvat. But the police declined to present the statement in court, bizarrely arguing that "it is at odds with the police investigation".