According to him, it is illegal for the president to appoint judges without reference to Chief Justice Martha Koome.
At the same time, he argues that the judicial inquiry is conducting a similar role as court as the same could be done in an inquest.
"The action in constituting the Commission of Inquiry is interfering with the independence of the Judiciary under article 161 of the Constitution of Kenya which provides that "In the exercise of judicial authority, the Judiciary shall be subject only to this Constitution and the law and shall not be subject to the control or direction of any person or authority," argues Mwangi.
Ruto last week tasked a judicial commission of inquiry with the responsibility of unearthing the truth behind the activities of the Makenzi-led Good News International Church, including persons and organizations who bear the greatest responsibility for the massacre of more than 100 people in Shakahola, Kilifi County.
The Shakahola Commission will be chaired by Lady Justice Jessie W. Lesiit and feature Lady Justice (Rtd) Mary Kasango, politician Eric Gumbo, Bishop Catherine Mutua, Jonathan Lodompui, Frank Njenga Dr Wanyama Musiambu and Albert Musasia.
Lawyer Kioko Kilukumi will be the lead counsel assisted, by Vivian Janet Nyambeki and Bahati Mwamuye. Joint Secretaries will be Oliver Kipchumba Karori and Rachel Maina.
"The mandate of the Commission of Inquiry shall be to inquire into the matter of the deaths, torture, inhumane and degrading treatment of members and other persons linked to the Good News International Church in Kilifi County," their TOR reads.
They will also inquire into the legal, institutional, administrative, security, and intelligence lapses that may have contributed to the killings and recommend specific actions that should be taken against those responsible including admonition, regulatory actions, reparations, or criminal investigation.
The team will recommend legal, administrative, or other forms of accountability action against any public official whose actions or omissions are established to have willfully or negligently contributed to the occurrence of the massacre.
Also, to inquire into the factors that led to the rise of that particular religious' extremist institution and suggest reforms to prevent the recurrence of the same. Both teams, whose mandates appear to overlap in a way, have six months to complete their tasks.
In setting up the inquiry, Ruto said the scale of the death toll and the depravity of the actions committed against fellow citizens in Shakahola had shaken the consciousness of the nation and brought to the fore the reality of the existence of cults of serious harm to Kenyans.
President Ruto invoked Section 3 (1) of the Commissions of Inquiry Act (Cap. 102) that informed his decision.
However, the Azimio leaders assert that the appointments are unconstitutional as it will also subject those implicated to double criminal process.
In his supporting affidavit, Raila argues that the President is acting the judge , the jury and the executioner as his appointees are likely not to give a fair verdict.
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According to him, the appointment for a judge or a magistrate should be by the CJ while the lead lawyer should be under the DPP.
At the same time, he argues a commission cannot force the Public Service Commission (PSC) to discipline any public official found culpable or negligent.
He accuses Ruto of overreach, stating that he is now forcing independent offices to conduct their work. The former Prime Minister has listed at least 13 prayers, among them to declare the appointments as unconstitutional and disband the team.
Azimio has sued the President, Attorney General, Speaker of National Assembly, Inspector General of Police, the National Intelligence Service, DPP and PSC.
He has also listed Kenya National Human Rights Commission and Commission on Administrative Justice as interested parties.