A government commission investigating the fatal shooting of 34 striking miners by South African police at the Marikana mine said the police force has lied, withheld documents and apparently doctored other papers.
In a statement, the Marikana commission said it had to search computer hard drives of officers to discover documents about the 2012 shootings that shocked South Africa and recalled the worst excesses of the apartheid era.
The commission said documents show the police version of events at the platinum mine "is in material respects not the truth".
The statement said the thousands of pages of new evidence include documents the police had previously said did not exist and material which should have been disclosed earlier by police. The commission adjourned until Wednesday to study the new evidence.
"We recognise that it is important that the SAPS (South African police) should have the opportunity to explain the matters which have raised our concern," the commission said. "However, we have to say that absent a convincing explanation, the material which we have found has serious consequences for the further conduct of the work of this commission."
Evidence presented to the commission has indicated some miners were shot in the back as they tried to flee and others were killed when they already were wounded and posed no threat.
Police, however, said they opened fire after striking miners attacked them. And South Africa's police chief, General Riah Phiyega, told the commission that officers involved in the shooting deaths were just doing their job.
A recent bout of unrest at South Africa's gold mines ended peacefully, with workers and management agreeing to a compromise on wage increases.
But the protests undercut productivity in a country that was already struggling with falling commodity prices as well as an unemployment rate of about 25%. Auto workers and municipal power workers in Johannesburg have also held protests, contributing to one of the biggest waves of labour unrest in recent years.
The Marikana killings deepened scepticism in some circles toward the ruling African National Congress party, the former liberation movement that has dominated politics since the end of apartheid and remains the overwhelming front-runner ahead of elections next year.