South African police lied, withheld documents and apparently doctored other papers during a government-appointed investigation of the police killings of 34 striking miners last year, a state panel said Thursday.

The revelation by the Marikana Commission of Inquiry is bound to heighten concerns about the police force which is struggling to stem high crime rates, and points to wider concerns among some South Africans who believe the nation has not lived up to the high expectations that prevailed when all-race elections were held for the first time in 1994 to end white minority rule.

The commission said it had to search computer hard drives of officers to discover documents about the August 2012 shootings that shocked South Africa and recalled the worst excesses of white-led apartheid rule, when mass killings such as those at Sharpeville in 1960 and Soweto in 1976 helped shape a protest movement forged through loss.

In last year's labor unrest, violence during strikes at Lonmin PLC's platinum mine near Marikana, northwest of Johannesburg, led to the deaths of 46 people, including the nearly three dozen miners who were shot dead by police.

The police version of events of the shootings "is in material respects not the truth," said the commission after studying the newly obtained documents.

The commission, which has faced delays as well as funding shortfalls, 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 the South African police, known by the acronym SAPS. The panel adjourned until Wednesday to study the new evidence, and said technicians were "continuing the painstaking and slow task of identifying and copying" hard drive material on police computers.

"We recognize that it is important that the SAPS 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."

The Associated Press telephoned police spokesmen to ask for reaction to the commission statement, but the officials were not immediately available.

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, Gen. 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 percent. Auto workers and municipal power workers in Johannesburg have also held protests, contributing to one of the biggest waves of labor unrest in past years.

The Marikana killings deepened skepticism 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. But discontent over a lack of opportunities and corruption scandals, as well as a more robust opposition, have eroded support for the ANC in some areas.

Nelson Mandela, the former prisoner and president who once led the ANC, is 95 years old and in critical condition at his home, where a team of doctors is caring for him around the clock.