A retired CIA agent who died on March 30 told a filmmaker that he gave the tip that sent former South African president Nelson Mandela to prison in 1962.

According to The Sunday Times and the Daily Mail, 88-year old Don Rickard told filmmaker John Irvin that he took action because Mandela, who became one of the world’s most revered leaders after his release in 1989 and his subsequent presidency, was “the world’s most dangerous communist outside of the Soviet Union.”

“We were teetering on the brink here and it had to be stopped, which meant Mandela had to be stopped,” Rickard is quoted in the Daily Mail. “And I put a stop to it.”

Rickard said he did not regret his decision, and that he feared Mandela would create the opportunity for the Soviet Union to invade South Africa and cause problems in the region.

After being released in 1989, Mandela became famous for his peaceful opposition to the racist apartheid policies of South Africa. He won the Nobel Peace Prize in 1993 and became the nation’s president in 1994.

After Mandela’s death in 2013 at the age of 95, The Los Angeles Times noted that while he was well known for his peaceful opposition to apartheid, Mandela’s leadership in the decade leading up to his arrest included support for violent opposition to South Africa’s leaders.

The CIA has never admitted involvement in Mandela’s arrest and imprisonment. The Daily Mail reports that Rickard retired from the CIA in 1978, but that his official bio does not mention the CIA, but instead his time as a diplomat for the U.S. government.