The EFF's Dali Mpofu has questioned Terror Lekota's allegation that Cyril Ramaphosa sold out his struggle comrades in the 1970s.
The EFF national chairperson said the timing of Lekota's accusation was suspicious.
Mpofu said that Lekota's reasons for making the statement needed to be examined.
Lekota made the bombshell allegation earlier this week in Parlimanet. He claims that Ramaphosa told apartheid police that his comrades were spreading "communist ideas".
In exchange for this information, Lekota says Ramaphosa received a lighter jail sentence.
Ramaphosa has since denied the accusation.
While the EFF initially cheered Lekota's accusation and gave him a standing ovation in Parliament, even offering Lekota their speaking time to elaborate on his claims, Dali Mpofu has since expressed doubt about the COPE's leaders statement.
Mpofu said the public should ask why Lekota had kept quiet for so long, and even compared to former Bosasa executive Angelo Agrizzi. He didn't outright accuse Lekota lying, but he insisted that the COPE leader was not an "overnight hero" to the EFF.
He reiterated that the EFF had applauded Lekota for sharing information with the public, but said that did not automatically mean that the party believed him.
This comes after Julius Malema wrote to Ramaphosa, asking the president to appoint a commission of inquiry to investigate the claims about his alleged collaboration with the apartheid regime.
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