Johannesburg - The NPA would not be drawn to comment on Thursday on why an investigation into prosecutors working on the Jackie Selebi case has dragged on for two years."Well, how long should it take then? Two years is not long," National Prosecuting Authority spokesperson Bulelwa Makeke told Sapa.She could not say when it would be completed."You can never say, I don't know when it will be completed."Netwerk24 reported on Thursday that Gerrie Nel and his team, which were members of the now disbanded Scorpions, were among the prosecutors being investigated.Some irregularitiesMakeke would only say that complaints were laid in 2012 relating to the Selebi case."If people make complaints against prosecutors, those complaints have to be investigated. It is a due process," she said, declining to specify if it was one complaint or more."There were some irregularities that people raised."Selebi was jailed for 15 years in 2010 after being found guilty of corruption. During his unsuccessful appeal application, Selebi insisted there had been a conspiracy against him. He was granted medical parole and died on 23 January at 64.The City Press on Sunday reported that former president Thabo Mbeki publicly questioned the NPA's investigation of Selebi.Mbeki wrote a tribute to Selebi which was read out at his funeral in Pretoria on Saturday by former diplomat and security advisor Welile Nhlapo.Conspiracy theoryMbeki reportedly alluded to elements in the country's law enforcement agencies who, he said, plotted to have Selebi unseated as commissioner."On 14 June 2013 at least one of our newspapers quoted an article under the heading: 'Agliotti: It was me or Selebi'," Mbeki said in his tribute."The newspaper quoted Mr Glenn Agliotti as having said: 'In fact, when the Scorpions took me in the foyer of my own house, the officers said I am arresting you for the murder of Brett Kebble and then said that if you give up that top cop Jackie Selebi, we will give you a section 204 immunity."I asked if I do, who are you going to arrest for killing Kebble then? That's how obvious the whole plot was that it was never about me, it was never about Kebble, it was a feud between one law enforcement agency wanting to bring down the most powerful policeman in Africa'."According to the newspaper, Mbeki also said he was pleased to read that the NPA was conducting an internal investigation regarding Selebi's prosecution."It's my fervent hope that the NPA really does indeed carry out an honest and thorough investigation into this matter, and not bury it simply because Jackie will have been buried," he said.