Former security policemen Brigadier Willem Schoon and Colonels Abraham Grobbelaar, Jan Coetzee and Christiaan Rorich appeared in connection with the incident involving the so-called "Cosas Four" on Monday.
Askari Ephraim Malapitsa, who was not present on Monday, is due to take the stand on Tuesday. An askari was an ANC cadre turned police informant.
The five have applied for amnesty for the murders of Bimbo Madikela, Ntshingo Matabane and Fanyana Nhlapo, and the attempted murder of Zandisile Musi, as well as damage to property on February 15, 1982.
Former Vlakplaas death-squad camp commander Coetzee (not Dirk Coetzee) told Judge Denzil Potgieter and advocates Leah Gcabashe and Chris de Jager at the Central Methodist Church in Johannesburg that Malapitsa turned himself in to the police after receiving military training in Eastern Europe.
He then came to Coetzee and told him he had met the younger brother of two other ANC cadres he went overseas with. He said the young Congress of SA Students (Cosas) member and his friends wanted weapons and training to kill a security policeman named Warrant Officer Mkosi and a council member.
He later said they had a sketch plan of houses they wanted to attack.
Coetzee said he decided it would be best to kill the activists instead of arresting them, to protect Mkosi and family members and to hide the fact that Malapitsa had turned and was now an askari.
"Askaris played a valuable role in identifying ANC cadres," Coetzee said.
He then went to Schoon for permission to kill the youths. Schoon agreed to the plan to protect Mkosi and Malapitsa, and to avoid anarchy and chaos.
Schoon in turn got permission from Brigadier Jan du Preez, who is apparently now too ill to appear at the hearings.
Grobbelaar, who attended the hearing in a wheelchair, said he went to the abandoned mine with Coetzee, Rorich and one of his own men, who had since died, so he could keep watch for any people walking by who could get hurt.
Rorich, who was a warrant officer and explosives expert serving in Ermelo at the time, said he placed a kilogramme of army explosives called PE4 in the pumphouse. His orders were to make the incident look as though the youths had blown themselves up.
Rorich said a minibus arrived in the dark and men got out and went into the old pumphouse, while the police hid in another building nearby. When Malapitsa made an excuse to the four activists and came out of the pumphouse, Rorich turned the detonator.
Three of the teenagers were killed, but Musi, survived the explosion. He is due to give evidence at the amnesty hearing.
Commissioners and lawyers repeatedly asked the four former security policemen if they knew how old the teenagers were, if they knew for a fact they were terrorists and if they had thought of any alternative plans other than murder. They also asked if the main aim of the scheme was not rather to kill the youths than protect anybody.
The former policemen all said they did not know details about the youths and that their main aim had been to protect their own.
The youths had no training or weapons and went with Malapitsa to start their training and obtain pistols and grenades, the lawyers said.
Grobbelaar made a heartfelt apology to the relatives of the dead teenagers at the hearing.
Other security police seeking amnesty for abductions and murders, including the killing of civil rights lawyer Griffiths Mxenge and the kidnappings of Herbert Mboli and Joe Pillay, will appear before the amnesty committee over the next three weeks.