South African authorities have charged 270 miners in the killings of 34 fellow workers, even though police are believed to have fired the fatal shots.

The workers were arrested after the deadly clash with police and were charged under a common-law provision that faults them for being involved in the clash.

Police spokesman Dennis Adrio said that some of those killed in the clash had gunshot wounds in their backs and that weapons were recovered at the scene.

The August 16 clash happened after negotiations between striking miners and the mining company broke down and police decided to fence in machete-armed protesters with barbed wire, according to police.

The protesters moved toward police and were driven back with tear gas and rubber bullets, and officers resorted to live ammunition when protesters attacked, police have said.

Police gunfire killed 34 people and wounded 78.

Thousands of machete-armed workers were striking for higher wages in the Lonmin mine in Marikana, South Africa, when police opened fire on their gathering. Earlier, two police officers had been hacked to death. The violence exploded when police shot at striking rock drillers in the “Easterns” area of the Marikana mine.

Tensions have been high in part because of the presence of competing trade unions: the Association of Mineworkers and Construction Union (AMCU) and the National Union of Mineworkers (NUM).

The mine, about two hours northwest of Johannesburg, is operated by Lonmin, which is listed on both the London Stock Exchange and Johannesburg Stock Exchange, and is the world’s third-largest platinum producer. The bulk of its 28,000 employees work at the mine, and around 23% belong to the AMCU.