"I saw her killing Stompie," said witness Katiza Cebukhulu, pointing a finger at Madikizela-Mandela.
Cebukhulu was flown out from London to give evidence at the Mayfair, Johannesburg TRC hearing into alleged atrocities and murders committed by the Mandela United Football Club, a gang of anarchical youths who acted as Madikizela-Mandela's bodyguards in the 1980s.
Cebukhulu, whose sensational accusations against the ANC Women's League president gained wide publicity when published in a book, "Katiza's Journey", by British journalist Fred Bridgland, was accompanied by former British Conservative Party MP Dame Emma Nicholson, who has taken him under her wing.
He further alleged he saw her assault another young activist, Lolo Sono, with a sjambok before Sono disappeared nine years ago.
Cebukhulu's testimony, coming on top of witnesses portraying President Nelson Mandela's former wife as a vengeful, violent woman deeply implicated in the assault and murder of several people, was expected to be a grievious body blow to Madikizela-Mandela's political career.
But Cebukhulu's evidence was halting and hesitant and contained several contradictions. And when discrepancies between the book and his statements were pointed out during cross-examination by TRC questioners and Madikizela-Mandela's lawyer, Ishmail Semenya, the witness was forced to concede that the book itself was inaccurate.
Nicholson was not perturbed by her ward's shaky testimony, she said after the protracted hearing on Tuesday.
Asked by reporters if she believed Cebekhulu's claims that Madikizela-Mandela stabbed Seipei, Nicholson answered: "I have believed his story for some time. However, I took it on spec. I was in no position to test all the points Katiza Cebukhulu made."
She said it took "considerable courage" for Cebekhulu to testify on Tuesday.
When Truth commissioner Yasmin Sooka said the book "Katiza's Journey" was filled with inaccuracies, her statement was greeted with applause from people in the public gallery, including Madikizela-Mandela.
Sooka said Cebekhulu's credibility was put at risk by the inaccuracies in the book, which opens with a description of Cebukhulu arriving at the Shell House headquarters of the African National Congress in Johannesburg, long before the organisation moved into the building.
Cebekhulu said Seipei was murdered several days after the activist was abducted from the Soweto manse of Methodist minister Paul Verryn and severely beaten by Madikizela-Mandela, Mandela United Football Club "coach" Jerry Richardson and others in December 1988.
Cebekhulu, who was living on Madikizela-Mandela's property at the time, said he heard her say at some time during the beating: "You are sleeping with a white man." Cebekhulu said he also heard Madikizela-Mandela accuse Seipei of being a "spy and impimpi".
Several days after the alleged kidnapping, Cebekhulu said he was returning from the toilet to his back room at Madikizela-Mandela's house after midnight when he saw her and others standing in the jacuzzi room.
"I saw Richardson walking towards the room with something, a person, in his hand. I don't know the person, but it was a person. Later I found out it was Stompie. Then I saw Mandela's wife raising up her hand twice."
Asked by advocate SL Joseph what was in Madikizela-Mandela's hand, Cebekhulu said: "It was something that was shiny."
Asked to clarify what he meant by "raising up her hand", Cebekhulu made stabbing motions. "She was stabbing. She stabbed twice," he said.
Earlier, Cebekhulu said he saw Madikizela-Mandela, Richardson and others brutally assault Sono while he lay helpless on the concrete garage floor of Madikizela-Mandela's Diepkloof home early in November 1988.
He described in detail how he saw Madikizela-Mandela whip Sono with a sjambok. Cebekhulu said Sono was lying on the floor trying to protect his head as Richardson kicked him and other members of the Mandela United Football Club formed a circle around the prone youth.
Cebekhulu said he last saw Sono bleeding from his mouth and left before the beating was over.
Later Cebekhulu was asked to accompany Madikizela-Mandela, Richardson, an injured Sono and one other to the Meadowlands home of Nicodemus Sono, Sono's father.
There, according to Cebekhulu, Nicodemus recognised his son and begged for his life, but Madikezela-Mandela said to him; "The movement will see what to do with him."
Cebekhulu said he was dropped off at Madikezela-Mandela's house and she drove off in the vehicle with Sono still inside it.
Nicodemus Sono, who testified on Monday, told the TRC he never saw his son again after this incident.
On Monday night Madikizela-Mandela laid charges of crimen injuria against Cebekhulu and two other over allegations about her in Bridgland's book.
Cebekhulu is a former Mandela United Football Club member and was Madikizela-Mandela's co-accused in the 1991 trial for the kidnapping of Seipei.
TRC chairman Archbishop Desmond Tutu, responding to disquiet expressed by Nicholson, said Cebekhulu would not be arrested or prevented from leaving the country because of the charges laid by Madikizela-Mandela.
Earlier, witness Xoliswa Falati said her former friend and idol, Madikizela-Mandela, had the "blood of African children on her hands".
She alleged Madikizela-Mandela had an affair with security policeman Paul Erasmus, started the assault oered up assaults, and admitted to Falati she ordered the killing of activist Sicelo Dlomo.
She further alleged Madikizela-Mandela assaulted activist Maxwell Madondo and that Madikizela-Mandela's driver, John Morgan, had told her the bodies of murdered activists Sono, Siboniso Shabalala and others were dumped down a mineshaft near Johannesburg.
"My hands are not dripping with the blood of African children. I went to prison for her, for my leader. She was so much ungrateful," said Falati of her conviction for Seipei's kidnapping in 1991.
"She wants to be clean all the time because she wants to be a demigod. Making a cult out of a leader is always a mistake."
TRC commissioner Hanif Vally said Falati showed no regret for her part in the assault on the four youths, including Seipei, who were taken from Verryn's manse, or in a smear campaign against Verryn in which the priest was branded a homosexual who sodomised youths in his care.
Falati said she lied during the trial over Seipei's kidnapping and murder to protect Madikizela-Mandela.
"I was told by her to to protect her, I was flown to Durban (to) fabricate some story to protect her. Yours not to reason why. You have to take orders and do and die. That was our culture, to protect our leaders."
Vally said she did not fully explain her part in these events. Witnesses had testified Falati took part in the assaults on activists.
Falati then said, without admitting involvement: "I say I'm sorry to Father Paul Verryn and all the victims who were assaulted."
Former activist Pelo Mekgwe told the hearing on Tuesday both Falati and Madikizela-Mandela were present when he, Seipei, Thabiso Mono and Kgase were viciously beaten by members of the Mandela United Football Club at Madikizela-Mandela's home after their abduction.
He said Cebekhulu, Richardson, Jabu Sithole and Falati carried out the assault which left Seipei grievously injured.
He said Seipei was the worst injured and that his head was "soft and swollen".
He said Richardson took Seipei away the following night.
Tuesday's hearing, which lasted 12 hours, ended with Cebukhulu's evidence, which contradicted among others, testimony by Richardson that he, not Madikizela-Mandela, murdered Seipei by slitting his throat with a garden shears.
Asked by a journalist as she was leaving the venue if she felt vindicated, a smiling Madikizela-Mandela replied: "I feel good."