So what happens to state security thugs when a racist government gets overthrown?
They get hired by our government to help with racist oppression elsewhere:

In its effort to relieve overstretched U.S. troops in Iraq, the Bush administration has hired a private security company staffed with former henchmen of South Africa's apartheid regime.

The reliance on apartheid enforcers was highlighted by an attack in Iraq last month that killed one South African security officer and wounded another who worked for the subsidiary of a firm called Erinys International. Both men once served in South African paramilitary units dedicated to the violent repression of apartheid opponents. -- from Billmon, who has a lot more on the subject.