Machel’s widow Graca is married to Nelson Mandela

South Africa has launched a fresh investigation into the 1986 plane crash on its territory that killed Samora Machel, the president of neighbouring Mozambique who was a fierce opponent of the white apartheid government at the time.

Speculation has long persisted that apartheid-era security agencies brought the plane down to rid Pretoria of a hostile neighbouring president. But previous probes into the crash in rugged terrain near the border between the two countries have failed to bring to light conclusive evidence of this.

Paul Ramaloko, spokesman for South Africa’s special police investigations unit the Hawks, said on Wednesday the probe was being conducted jointly with Mozambican officials.

“I do confirm it and we are working with the Mozambicans on this,” he told Reuters, but he gave no further details.

Machel was a charismatic military commander and ardent Marxist who became Mozambique’s founding president in 1975 after the nation gained independence from Portugal, putting it on the front line in the struggle against white-ruled South Africa.

He was killed with 33 others in October, 1986, when the presidential aircraft, a Soviet Tupolev, crashed in mountainous countryside en route to Mozambique from Zambia.

South Africa’s Times newspaper reported on Wednesday the government had launched a new investigation because fresh evidence had emerged indicating the involvement of apartheid-era security officials. Apartheid ended in South Africa in 1994.

Ramaloko, asked if the inquiry would focus on government officials or security forces under apartheid, said: “I really cannot say who will be implicated, or if they are still alive.”

Regional tensions were running high at the time of the crash. Mozambique was in the throes of a civil war, in which South African-backed Renamo rebels were fighting against Machel’s government and ruling Frelimo party.

In 1987, a South African judge concluded the crash was caused by pilot error on the part of the Soviet crew.

Following the end of white minority rule, South Africa’s Truth and Reconciliation Commission, set up to look into political crimes in the apartheid era, launched an inconclusive probe into the crash and said further investigation was needed.

Machel’s widow Graca married Nelson Mandela in 1998 while he was still president of South Africa.

Mandela, who retired in 1999 and is now 94, on Wednesday was spending his fifth day in a Pretoria hospital where he is being treated for a lung infection.