Former CIA agent Donald Rickard said he tipped police off to Mandela's whereabouts, which led to the former statesman spending the next 27 years of his life behind bars.
The ex-spy didn't seem regretful about his actions, calling Mandela "the world's most dangerous communist outside of the Soviet Union" in an interview with British filmmaker John Irving earlier this year.
"That revelation confirms what we have always known, that they are working against [us], even today," African National Congress spokesman Zizi Kodwa told BBC Africa. "It's not thumb sucked, it's not a conspiracy [theory]."
Rickard previously denied the allegations in a 2012 interview with The Wall Street Journal.
"It's not true. There's no substance to it," he said at the time.
Rickard died in March.