In act 2, scene 5, who massacred the Balubas?

The Baluba tribe has been in conflict with the Katanga independence movement. Katanga is a diamond-rich province in Congo, and despite the country having gained independence, the colonial powers still want to exert some kind of control over the country in order to continue exploiting its enormous mineral wealth. The colonial powers provide funds and weapons for the Katanga independence movement, hoping to maintain the existing supply of diamonds.
The Baluba have close tribal relations with the leader of Congo, Patrice Lumumba, so they are naturally hostile to the Katanga independence movement. Inevitably, war breaks out, and terrible atrocities are committed on both sides. One such atrocity occurs on October 1960 when foreign mercenaries, in conjunction with Katangan police, carry out a massacre of large numbers of Baluba as well as the wanton destruction of entire villages.