In 1960 two thirds of the 69 people killed during peaceful anti apartheid march were shot in the back what does this suggest happened

Government targeted protesters 

If protesters were shot in the back, that suggests they were not shot in self-defense or in a confrontation but rather as they ran away or were being peaceful. 

This evidence could support that the protesters were massacred by the government through the police forces. Being shot in the back suggests it was peaceful and protesters were not fighting back when shot.