By Peter Biles
BBC News, Johannesburg
The South African government is trying to solve one of the great mysteries of the apartheid era - the 1986 plane crash that killed President Samora Machel of Mozambique.
Samora Machel died returning from a trip to Zambia
He died when his aircraft hit a mountainside in South Africa, close to the Mozambique border.
There has long been speculation that the crash was caused by sabotage, masterminded by the white apartheid state.
The South African authorities are currently conducting a new investigation into what happened on the night of 19 October, as President Machel and his entourage returned from a summit in Zambia.
The National Prosecuting Authority (NPA) has confirmed that a fresh probe is under way.
The NPA refuses to say when it will be completed, but it is understood that the enquiry should be wrapped up before the end of the year.
SAMORA MACHEL 1933-86
1960s: Led Mozambique guerilla campaign against Portuguese colonial rule
1975: Became Mozambican president
Oct 1986: Killed in plane crash
In his weekly newsletter, ANC Today, South African President Thabo Mbeki has paid tribute to the late Samora Machel, describing the founding father of independent Mozambique as a "towering giant of the African Revolution".
However, President Mbeki says one question remains unanswered - was the apartheid regime responsible for the tragic deaths at Mbuzini where the plane came down?
South Africa's foreign minister at the time, Pik Botha, was one of the first VIPs to arrive at the crash site.
Looking back, he says it was one of the worst days of his life.
"The scene was absolutely shocking," Mr Botha recalls. "Parts of the aircraft and bodies were strewn everywhere.
"I asked to be shown the body of the person whom the police thought might be the Mozambican president," Mr Botha says.
"They opened a bag. The zip made a terrible noise. I had known Samora Machel very well. I immediately recognised his face, even though his head was severely damaged".
The months preceding the crash had been a time of rising tension in southern Africa. Mozambique's civil war was getting worse.
South Africa had reneged on the Nkomati Accord, a non-aggression pact signed in 1984.
Mozambique kept its side of the agreement by forcing ANC exiles to leave the country, but Pretoria soon resumed its support for the Renamo rebels fighting the Frelimo government in Mozambique.
In the meantime, Malawi had been collaborating with white South Africa by aiding Renamo.
The situation came to a head when President Machel threatened to deploy missiles on his border with Malawi.
Dan Moyane, a South African-born journalist who worked in Mozambique in the 1980s, had initially been offered a seat on Machel's plane in order to report on the summit in Zambia.
However, he was bumped off at the last moment when more members of the government delegation were required to travel.
Moyane recalls the sense of shock when the news of Samora Machel's death in the plane crash was confirmed.
"There was stunned silence in Maputo. A sense of disbelief. And then we began asking questions - who was on the plane, who didn't fly?"
The South African-appointed commission of inquiry, headed by Justice Margo, blamed the Russian pilots of the Tupolev Tu-134.
But in Mozambique, the findings did nothing to remove the suspicion of foul play.
In 1998, South Africa's Truth and Reconciliation Commission (TRC) launched a special investigation into Machel's death.
President Machal's widow, Graca, later married Nelson Mandela
However, it was unable to reach a firm conclusion and said that a number of questions had been raised, including the possibility of a false beacon.
Ambassador Abdul Minty, South Africa's Deputy Director General of Foreign Affairs, who worked with the British Anti-Apartheid Movement for three decades, gave evidence to the TRC and remains convinced that a decoy beacon caused the plane to crash.
"From the research I've done, my understanding was that an electronic decoy was utilised to give the pilots false information about the maps and the region," Mr Minty says.
"It could have been carried in a small backpack, or even planted. My interpretation is that this would have confused the pilots and led them into the mountains."
The plane had been on its approach to Maputo, but veered off course, and crashed a few hundred metres inside the South African border.
Mr Botha argues that the issue of a decoy beacon was specifically investigated, and found to be technically impossible.
He says there has been no firm evidence to suggest anything other than pilot error as the cause of the crash.
But while drawing different conclusions from Mr Minty, the two men agree on the need for the latest South African investigation to bring closure on the affair.
"The people of Mozambique, including Graca Machel and her family, need to know what happened," says Mr Minty.
"We in the anti-apartheid struggle need to know. It's part of our history, so it's critically important to establish the truth".