Pretoria - A third Boeremag member, Brits engineer Rooikoos du Plessis, was convicted on a charge of high treason on Monday.
Judge Eben Jordaan convicted brothers Mike and Andre Du Toit on the same charge last week.
On Monday, he found that Du Plessis had actively taken part in planning a violent rightwing coup and the military take-over of the government.
He was also a member of the inner circle of the Boeremag.
Du Plessis had attended numerous meetings in 2001 at which the coup was discussed and had travelled all over the country to recruit supporters.
He was also the main speaker at many meetings where he discussed the visions of Boer prophet Siener van Rensburg to drum up sympathy.
He often played songs by Afrikaans singer Koos du Plessis, whom he called a visionary.
Du Plessis's usual speech was to warn that blacks would go “on the rampage” and kill whites when former president Nelson Mandela died and that whites had to be ready to defend themselves.
At later meetings, Du Plessis openly talked about a coup and about taking over military bases.
He also talked about the new government and said a Boer court would be formed after the coup that would try “traitors”, such as former president FW de Klerk and former military commander General Constand Viljoen.
Some of the discussions centred around keeping attack helicopters on the ground during the coup and shooting pilots if necessary, or destroying the aircraft to stop resistance during the coup.
Placing sharpshooters around airports and shooting down a Boeing to create chaos were also discussed.
Jordaan said Du Plessis had been involved in discussions about the formation of so-called shadow commandos.
It was his idea that the commanders of commandos should be involved in the coup plot.
Where they were not sympathetic, shadow commandos should be formed.
He told witnesses he needed 8000 commando members for the coup.
Later, after his house was raided by police in October 2001, Du Plessis carried on with his coup plans.
He was also involved in testing explosives with a view to blowing up electricity lines.
Du Plessis featured prominently in Document 12, the “war plan” drawn up by Mike du Toit, which set out the coup plan in detail.
Jordaan said after Du Plessis withdrew his involvement in the coup plan late in October 2001, he did not tell authorities about the plot.
Jordaan's summary against the 20 accused is expected to take up to another two weeks or longer to complete. - Sapa