Judge Eben Jordaan said in the North Gauteng High Court in Pretoria there was no doubt that Andre du Toit, a former policeman, had been part of the inner circle of the Boeremag organisation which had planned a violent rightwing coup to overthrow the ANC-led government.
Mike was convicted of treason on Thursday.
Andre had attended numerous meetings with Mike in various parts of the country where the coup was planned and discussed in 2001 and early in 2002.
He was also present at a meeting in January 2002 when he swore allegiance to the Boeremag and its cause and was handed a bullet as symbol that "traitors" would be shot.
The plans entailed creating chaos in the country through a trigger event, whereafter military bases would be taken over, the government replaced with white military rule and all blacks and Indians chased out of the country.
Blowing up the Vaal dam, shooting down a Boeing and blowing up power stations were among the plans discussed.
Specific tasks were assigned to people at some of the meetings.
The judge accepted evidence that Andre du Toit had been placed in charge of communication in continuation of the coup plan while he and his brother were already on the run from police late in 2001.
He was also one of the accused who had handed a military radio to a police agent during a meeting at a strip club in Pretoria.
The agent had infiltrated the organisation and later testified against him.
According to the evidence, Andre had discussed his fears that the man might be a police spy with another state witness but his older brother Mike did not share this view.
No turning back
One of the most important pieces of evidence against Andre was a conversation with the same agent that was taped and later played in court during the trial.
In the conversation, he made it clear that there was no turning back and remarked how wonderful it was that there were people supporting their plan.
He also talked about taking over the military bases as Lohatlha and Kimberley.
Andre was present when explosives were tested at a place near Bela Bela with the aim of blowing up power lines and substations.
The court rejected his claims that the meetings he attended had been innocent and aimed at self-protection against farm attacks.
Judgment will continue on Monday. – Sapa