Maputo — The Mozambican state has reaffirmed its determination to use all necessary means to clarify the exact circumstances under which the country's first President, Samora Machel, died on 19 October 1986, in a plane crash at Mbuzini, just inside South Africa.

A press release issued on Sunday by the office of President Armando Guebuza to mark the 22nd anniversary of the disaster declared "Discovering the truth about the death of President Samora Machel remains a priority for the Mozambican nation".

It has long been believed that the crash of the presidential aircraft, a Soviet-manufactured Tupolev 134, was no accident. The cockpit voice recorder showed that the highly experienced Soviet crew made a fatal turn to the west, because they believed they were following the navigational beacon at Maputo airport. While the pilot believed the aircraft was descending towards Maputo, in fact it was flying away from the Mozambican capital towards the hillside at Mbuzini, where it crashed, killing Machel and 33 others.

The question has always been: what beacon was the Tupolev following? It is widely suspected that the apartheid military had installed a pirate beacon, broadcasting on the same frequency as the Maputo beacon to lure the aircraft to destruction.

Immediately before the crash, tensions had risen sharply between South Africa and Mozambique. The Nkomati non-aggression pact between the two countries lay in ruins, since the apartheid military had continued to arm the Renamo rebels. In the weeks prior to Machel's death, South African Defence Minister Magnus Malan had publicly threatened the Mozambican leader.

Predictably the South African authorities refused to cooperate with any investigation into a possible pirate beacon. Instead they held their own unilateral commission of inquiry, under apartheid judge Cecil Margo, which reached the pre-ordained conclusion that the Soviet pilot was to blame.

Mozambique never accepted this conclusion, but nothing further could be done until the fall of apartheid. But when South Africa's first democratically elected president, Nelson Mandela, made his first official visit to Mozambique, in July 1994, the government gave him a copy of its dossier on Mbuzini.

However, investigations by South Africa's Truth and Reconciliation Commission proved inconclusive and over a decade later, in August 2005, Guebuza, in contact with his South African counterpart, Thabo Mbeki, stressed Mozambique's interest in reactivating the investigations.

According to the Sunday release, Guebuza also sent an envoy to deliver all pertinent documentation to Mbeki, and to discuss with the South African government the best ways of moving the case forward.

The release revealed that, "in order to give a new dynamic to the investigations", Guebuza, in May 2008, handed the dossier over to Attorney-General Augusto Paulino - the first sign that criminal charges might eventually be pressed. Paulino subsequently set up a team, headed by himself, which is looking into the dossier.

Interest in the crash has also been revived in South Africa, where the South African Broadcasting Corporation (SABC) transmitted a programme on Machel's death, which included testimony from Hans Louw, a former agent of the Civil Cooperation Bureau (CCB) which, despite its innocuous name, was one of the death squads set up by the apartheid security services.

Louw was part of a back-up team sent to Mbuzini to make sure that Machel was dead. If the plane had not crashed, he said, the group had a "Plan B", which was to shoot it down with a heat seeking missile.

The former apartheid foreign minister, Pik Botha, continues to insist that the regime in which he was such a key figure investigated the claims of a pirate beacon, and found no evidence to support them. Nonetheless, he told SABC that he thought the allegations could be cleared up by the creation of a new commission of inquiry.

Louw's story gains in force from the fact that the first people on the scene at Mbuzini were not the police or the emergency services, but the military, and they were much more interested in scouring the site for documents than in helping the ten survivors, most of whom were severely injured (and one of whom later died of his injuries).

The survivors noted nearby military tents, the presence of which the South Africans were never able to explain. Even the apartheid authorities had to admit that there was a large tent nearby, and that it was removed the day after the crash. The suspicion must be that this tent may have sheltered the pirate beacon (and perhaps the missile that was to be used if the initial plan went wrong).

There were no official commemorations of the anniversary of Mbuzini this year, but relatives and fiends of Machel laid flowers at his tomb, in Maputo's Monument to the Mozambican Heroes. The government preferred to celebrate Machel's life, rather than mark his death, and so the main ceremonies took place on 29 September, which would have been Machel's 75th birthday, had he lived.

Guebuza chaired these commemorations at Machel's birthplace in Chilembene, in the southern province of Gaza. Chilembene was then declared part of the country's cultural heritage.

Interviewed by Mozambican Television (TVM), Samora Machel's widow, Graca, said she remains convinced that her husband was murdered. She said she had spoken by phone with someone who claimed he had been at Mbuzini to shoot down the plane "if Plan A failed" (this person was presumably Louw).

Graca Machel said she is convinced there are people still alive who know the full circumstances of the plane crash - the difficulty, however, lies in persuading them to come forward as witnesses.

"This is the problem", she said, "since without evidence there can be no trial. It is not difficult to go to the depth of the truth, but the problem is finding someone who will testify in court".

Samora Machel's son, Samora Junior ("Samito"), interviewed by the independent television station STV, declared "Today, nobody doubts that my father was murdered".

More controversially, he believed there had been "an internal hand in the design of the plan to liquidate Samora Machel. Whether it was from Frelimo or from some other body, I don't know".

However, if the false beacon theory is accurate, the technology involved would not have required any Mozambican co-conspirators.