A key human rights organisation in South Africa launched an independent investigation into the police shootings on Sunday.
The Legal Resource Centre (LRC) said that it had obtained multiple witness testimonies that blame police brutality for the killings of strikers who were calling for pay raises.
Some witnesses have said that police shot protesters who were either trying to escape confrontations with police by hiding behind rocks, or while surrendering to authorities.
The LRC also said it has forensic evidence that suggests a police cover-up of the killings.
On August 16, police opened fire on a crowd of miners engaged in a strike at the Lonmin platinum mine in Marikana.
Video showed a densely packed crowd of miners, some armed with clubs and machetes, approaching heavily armed police, who claimed self-defence in the shooting.
The incident was the climax of an escalating stand-off between rival unions that had already killed 10 people, including two police officers.