Hein Grosskopf, a former liberation fighter, has revealed for the first time how he detonated a car bomb at the Witwatersrand Command army base in Johannesburg in July 1987.

Months of planning went into the attack, which was a one-man operation, Grosskopf told the Truth and Reconciliation Commission in Pretoria on Tuesday.

Grosskopf, 36, testified that he rented a house in the rightwing town of Ventersdorp as an operational base, but he left the town after suspecting that his cover might have been blown.

Now living in the United Kingdom, Grosskopf is seeking amnesty for the explosion on July 30, 1987.

Twenty-six people, mostly civilians, were injured in the blast.

Grosskopf, the son of Johannes Grosskopf, a former editor of the Beeld newspaper, said he joined the African National Congress in exile in 1986 after concluding that apartheid was reprehensible.

He linked up with the ANC in Lusaka, where he volunteered for military service.

After undergoing training in Angola, he returned to Lusaka at the end of 1986.

"It was agreed that I would be deployed in special ops as a single operative, and I was moved to an underground residence," Grosskopf said.

The next six months were spent on planning his infiltration back into South Africa, and selecting a target. Wits Command was chosen after much deliberation.

Grosskopf said: "Because the state had so clearly politicised the role of the SA Defence Force by deploying troops in townships, SADF personnel and installations were by definition justifiable targets."

The explosion was planned to go off by 9.45am, when the morning rush-hour was over, children would be in school and restaurants around the site were still closed.

Grosskopf said it was agreed that a car with an automatic gearbox should be used. By lashing the steering wheel in a fixed position, the car could be made to move without a driver towards the target.

In June 1987, Grosskopf entered South Africa on a motorcycle from Botswana.

"Along the way, I bought a Valiant bakkie in De Deur and travelled to Johannesburg with the cycle in the back of the van."

After booking in at the Holiday Inn in Pretoria under the name if JR Evans, Grosskopf rented a small flat in Linden, Johannesburg.

"From around 5 to 10 July 1987, I carried out further reconnaissance at Wits Command," Grosskopf said.

He found it would be possible to park in Quartz Street, opposite the target. He also measured the height of the pavement the attack vehicle would have to mount before reaching the wall of Wits Command.

After concluding that the operation was feasible, Grosskopf returned to Botswana and requested 120kg of explosives from his support group.

The load was hidden behind the seats of the bakkie, and steel plate was welded over it.

"Around July 17, I rented a house in Ventersdorp, intending to use it as an operational base. I believed that a single Afrikaner would be under less scrutiny in a small town than in Johannesburg's suburbs," Grosskopf said.

But as he was moving in, two policemen arrived and asked why his bakkie was registered in a name different from the one he used when renting the house.

Grosskopf said he spent only one night in the house before returning to Johannesburg.

Early on the day of the attack, he drove into Johannesburg on his motorbike and left it two street blocks from the target. He returned to the Linden flat by taxi.

Around 9am he left for Johannesburg after loading the explosives on the bakkie. The vehicle was parked in Quartz Street.

"With the car idling, I lashed the steering wheel in the required position. I threw all three switches, got out the car, locked it and walked towards Sterland (cinema complex)," Grosskopf said.

"Just before reaching the inside of the complex proper, I heard the Valiant's engine revving very fast and loudly, then a loud explosion that shattered all the glass in front of me."

By the time he reached the motorcycle, sirens could be heard all over Johannesburg.

"I drove back to Linden, collected some belongings and headed for Botswana on the motorcycle," Grosskopf testified. - Sapa