Speaking on an SABC radio programme, Mamasela said Mokhehle stayed at Vlakplaas during the early 1980s.
He denied that Mokhehle was ever used to kill South Africans. He said Mokhehle's mission at Vlakplaas was to be armed. He later went to Botswana where he saught political asylum.
Mamasela, an askari (African National Congress member turned police informer), testified against former Vlakplaas commander and convicted killer Eugene de Kock, who was sentenced by the Pretoria Supreme Court in October to two life terms in prison.
Mamasela said he was being harassed by some of the policemen who had applied for amnesty from the Truth and Reconciliation Commission. He named Paul van Vuuren as one of the policemen allegedly harassing him.
According to Mamasela, the Transvaal attorney-general had already issued an interdict preventing van Vuuren from harassing him.