President Jacob Zuma has vigorously defended his decision to appoint Menzi Simelane as National Director of Public Prosecutions (NDPP).

Zuma and Justice Minister Jeff Radebe on Thursday submitted their answering affidavits in the Democratic Alliance's (DA's) case to challenge Simelane's appointment.

DA leader Helen Zille filed papers at the High Court in Pretoria on December 11 to have Simelane's appointment declared unlawful.

In a founding affidavit, DA chairperson James Selfe said that the party was challenging Simelane's appointment as it was an objective jurisdictional requirement that he be a "fit and proper person" and have "experience, conscientiousness and integrity".

The party was also challenging Zuma's decision to appoint a new NDPP as an executive, rather than administrative action.

"It was unlawful, irrational, arbitrary, biased, based on an ulterior motive and inconsistent with the Constitution," Selfe said.

The basis of the party's argument against Simelane was that he gave "misleading and untruthful" evidence before the Ginwala inquiry established to ascertain the fitness to hold office of his predecessor Vusi Pikoli.

Former speaker Frene Ginwala's report was critical of Simelane, finding that his conduct as the then justice department director general was "irregular" and that his testimony was "contradictory and without basis in fact or in law".

The DA further submitted that Zuma's decision was not reasonable or rational and did not take into account the serious allegations against Simelane, both in the public domain and in the inquiry's findings.

In his responding affidavit, Zuma said his decision to appoint Simelane was not an administrative one and was made in terms of the Constitution and the National Prosecuting Authority Act.

In appointing Simelane, "I was exercising executive authority vested in me", he said.

"I deny that my decision was unlawful, irrational, arbitrary, biased, based on an ulterior motive and inconsistent with the Constitution."

Simelane also had all the legal qualifications and experience required by law for the position, and was indeed a "fit and proper" person.

"Whether a person is fit and proper to be entrusted with the responsibilities of the office concerned is my subjective decision.

"I am the person, as the President of the Republic, to be satisfied that the person is fit and proper.

"I made a decision that advocate Simelane was fit and proper with due regard to his experience, conscientiousness and integrity to be entrusted with the responsibilities of the office of the NDPP. I duly appointed him.

"In the premises, I submit that the decision to appoint Adv Simelane is lawful and in accordance with the Constitution."

Zuma said that the DA made "unsubstantiated allegations of a perceived threat" to the institutional independence and integrity of the prosecution services as a result of Simelane's appointment.

"I submit that these unsubstantiated allegations are intended to create unwarranted panic and hysteria over his appointment," he said.

Zuma admitted the Ginwala enquiry held that Simelane's conduct left much to be desired. "I point out, however, that the enquiry was specific as regards the testimony it rejected.

"It does not mean that the testimony of Adv Simelane was rejected in toto."

Simelane was merely a witness and his testimony was open to acceptance or rejection by the enquiry.

"Nowhere in the report does the enquiry find that he acted maliciously or with intent to mislead the enquiry," Zuma said.