Controversial Hawks head Major-General Berning Ntlemeza believes he has the authority to wield power over the National Prosecuting Authority and its decisions on what cases to prosecute and review.

Days after the Hawks' case against Independent Police Investigative Directorate (Ipid) boss Robert McBride and two of his subordinates collapsed in court last week, e-mails have emerged which show Ntlemeza last year questioning former NPA boss Advocate Mxolisi Nxasana's authority to review the case and demanding the docket be returned to him.

McBride and his co-accused - Innocent Khuba and Matthew Sesoko - appeared in court for allegedly altering a report into the involvement of former Hawks boss Anwa Dramat and Hawks Gauteng commander Major-General Shadrack Sibiya in the rendition of 12 Zimbabwe nationals back to their country in 2010 and 2011.

In Ipid's original report, Dramat and Sibiya were found to have been involved in the renditions, which saw two of the Zimbabweans murdered. None of the crime intelligence officers involved in the operation were ever prosecuted.

The two reports were reviewed by Sandile July of Werksman Attorneys, on instruction by Police Minister Nathi Nhleko.

It was July's refusal to testify about his review of the two reports - and the refusal of those he interviewed in his report to testify - that saw the case dropped.

The e-mails, sent in March last year, show that Ntlemeza gave Nxasana a 24-hour ultimatum to return the docket to him.

The e-mail was sent six days after Nxasana took the South Gauteng Director of Public Prosecutions Sibongile Mzinyathi to task for leaking an internal memo to Ntlemeza in connection with the case and for responding to an e-mail addressed to him by Ntlemeza.

In an e-mail sent on March 24 2015, in which Ntlemeza seems to question the authority of Nxasana's position, Ntlemeza said: "While we respect the processes of the NPA, it is unclear to us why was the docket handed to the NDPP [National Director of Public Prosecutions] in this matter as the prosecutorial decisions are made by the Directors of Public Prosecutions, nor why did the DPP decide not to inform us about his decision when it is clear that he has made it.

"We would appreciate [it] if we may get the docket and the NDPP decision at your earliest convenience but not later than the close of business on Wednesday, 25 March 2015."

Hawks spokesman Brigadier Hangwani Mulaudzi said the e-mail did not constitute interference. "The correspondence was of course communication between two heads of departments to clarify the delay, which was already impacting on the case and not to interfere with the administration of justice - since 2011 the case was not finalised."

He declined to comment on questions as to why no crime intelligence agents were investigated, despite being sent copies of congratulatory notes from the Zimbabwe crime intelligence office to their South African counterparts for a successful operation.

NPA spokesman Luvuyo Mfaka said the NPA exercised its prosecutorial discretion independently and no department could dictate to it how it must execute its mandate and exercise its discretion.

Ipid spokesman Moses Dlamini said the e-mail showed interference. "It confirms the conflict of interest due to the fact that both Hawks and Crime Intelligence officers were involved [in the rendition]. Hawks members were subjects of the investigation, so how do they justify demanding that they receive the docket?"

SA Policing Union president Mpho Kwinika said both the police and NPA were governed by separate acts which made them independent of each other. "You cannot have a head of one department making demands on the head of another."