11 June 1977
Almost a year after the June 16 Soweto Student Uprising, Security Police announced the arrest of Soweto Students' Representative Council (SSRC) leader Dan Sechaba Montsitsi. Four White students were also arrested for the same reason, namely plans to commemorate the Soweto uprisings.
References

Kalley, J.A.; Schoeman, E. & Andor, L.E. (eds)(1999). Southern African Political History: a chronology of key political events from independence to mid-1997, Westport: Greenwood.