The IPID boss claims that Nhleko is putting pressure on the police complaints body.
The four are suspected of being involved in the illegal rendition of Zimbabweans in 2010 – the same as Shadrack Sibiya and Anwa Dramat.
An inquiry into alleged UK complicity in the mistreatment of suspects will probe new claims that spy agency MI6 was involved in rendition to Libya.
Rights group Amnesty pressed Ireland on Tuesday over suspected CIA rendition flights through airports including transatlantic stopoff Shannon.
Binyam Mohamed, a UK resident held at Guantánamo Bay for more than four years, was released and put on a plane to home on Monday.
