Police in South Africa shot at least a dozen striking miners in the back during the so-called "Marikana Massacre” in August, lawyers said on Monday, undermining arguments that officers acted in self defence when they killed 34 people.Lawyers for the victims also told a South African investigation panel hearing opening statements on the August 16 shooting at Lonmin’s Marikana platinum mine that no police officers appear to have been injured in what was the deadliest security incident since the end of apartheid."(Evidence shows) that no less then 14 striking miners were shot from behind,” Dumisa Ntsebeza, a lawyer for families of 21 of those killed told the Marikana Commission of Inquiry. "That would be wholly inconsistent with the claims of necessity that the South African Police Service will advance.”If it is proved that the police did shoot miners in the back, it could be used by critics of President Jacob Zuma, who is facing an internal election at the end of the year to renew his leadership of the ruling African National Congress.The commission is expected to hear post-mortem reports on the 34 shot dead as early as Tuesday - the lawyers said they had already had access to the material.South African police said they had used force as a last resort and that all the shootings were justified in what was a swiftly shifting situation."The evidence will regrettably show that some of the protesters intended a bloodbath,” the police said in their opening statement.