Bloemfontein - The Supreme Court of Appeal (SCA) has reserved judgment after President Jacob Zuma and the National Prosecuting Authority conceded that former NPA head Mokotedi Mpshe's decision not to prosecute Zuma on corruption charges was irrational.Advocate Kemp J Kemp, SC, for Zuma, told the full bench of justices on Thursday that he believed that the NPA had erred in their decision. "Lets take it a step further - in other words, they made an irrational decision?" Justice Azhar Cachalia quizzed Kemp. "That is then correct, yes," Kemp replied. Seeking leave to appealZuma and the NPA have approached the SCA in Bloemfontein, seeking leave to appeal the 2016 decision by the North Gauteng High Court in Pretoria on the "spy tapes" saga. Kemp said that if the SCA finds that Mpshe did not make a rational decision, then someone would have to make a rational decision on that basis. "We will make decisions on what the law is, nothing more," Justice Mahomed Navsa said. During arguments, Navsa said, when Mpshe decided not to prosecute Zuma on the corruption charges, there had been no investigation into his decision. The long-standing matter was brought by the Democratic Alliance.'I am sorry to do this to you'Advocate Hilton Epstein, SC, for the NPA, faced tough questions from the visibly unimpressed judges, who pressed him on who had decided on whether Zuma should be prosecuted or not. Navsa said that those accused of grave crimes should go on trial."I am sorry to do this to you, Mr Epstein," Navsa said, as he pushed for answers. Navsa said, what needed to be weighed up was the reason for the decision not to prosecute Zuma, against the public interest. #Spytapes #SCA court is now in session @News24 pic.twitter.com/WpssCWTyyn— Jeanette Chabalala (@J_chabalala) September 14, 2017"There was no investigation that was achieved," Navsa said. "We are dealing with something different here; decision to prosecute," which he said was unchallenged. Navsa said the decision was a matter of "law and logic". But Epstein said, in this instance, the charges were withdrawn. Epstein argued that the timing of the charges against Zuma was aimed at manipulating who would become the president of South Africa. "Anybody who will be prosecuted will be prosecuted fairly," he said. Contradictory affidavitsHe asked the justices for direction on whether the charges should be reinstated or not. But Navsa pointed out that the court accepted it was its job to see if someone had overstepped the mark.However, Cachalia said contradictory affidavits were being put forward by the same NPA officials. "The heart of the decision in 2009 would have been before the decision makers," Cachalia said.Charges to be reinstatedThe 18 charges against Zuma were withdrawn in 2009, just before he was sworn in for his first term as president, but the DA wanted the charges to be reinstated.In 2016, a full bench of judges overturned the NPA's decision to drop the corruption charges against Zuma that related to fraud, racketeering and money laundering.Both the NPA and Zuma turned to the SCA after the High Court denied them direct access for an appeal.Both parties also defended the NPA's discretionary powers, labeling the DA's argument as off the mark.They said the DA's contention that the court could overturn the decision, but that the NDPP could not, was "wrong in principle and offensive to the powers of the NDPP and the NPA generally in deciding to prosecute or terminate a prosecution".