Speaking at a press conference in Parliament, Maimane, who was flanked by senior party member and MP Wilmot James, said: "Today we seek justice for the more than 100 South Africans – sons and daughters of this country – who died tragic and avoidable deaths at the hands of an uncaring, dysfunctional and unresponsive ANC [African National Congress] government in Gauteng."
He added: "As the Democratic Alliance, we cannot sit on our hands while the whole truth has yet to be exposed, and real justice has yet to be served. For this to happen, a Judicial Commission of Inquiry is very much required."
Maimane said the lives of those who died at the hands of government in this tragedy are of no less value than the victims of the Marikana Massacre: "If Marikana warranted a Judicial Commission of Inquiry – which it rightly did – then Esidimeni does too."
Maimane said less than one year ago, the Gauteng health department took a reckless decision to cancel its long-running contract with Life Healthcare Esidimeni – which looked after more than 2,000 mentally ill patients – without securing adequate alternative care facilities for these individuals.
"These helpless patients were then chaotically transferred to 27 NGOs – all operating without legal licenses – and many without the capacity and professional staff to handle the patients.
"Our Constitution, in Section 12(1)(e), gives everyone the inalienable right to not to be treated in a cruel, inhumane or degrading way. Regrettably, that is the apt description of how these patients were treated: cruel, inhumane and degrading."
Maimane said as a result more than 100 mentally ill patients lost their lives due to a "litany of judgment errors by the ANC government".
"Sadly, it could have been avoided, which is what makes it even more heart-breaking."
The DA leader said as far back as 2015, DA MPL Jack Bloom warned the Gauteng provincial government that a crisis was looming, but he was ignored.
"Instead, the ANC government stood by its decision and swiftly cancelled the contract with Life Healthcare Esidimeni – discarding thousands of human beings – and putting into motion this calamity."
He said the DA stands in solidarity with the family and loved ones of the deceased mentally ill patients, and maintains that it is absolutely critical that these events are thoroughly investigated, so as to avoid a repeat of such a tragedy.
"I have therefore written to President Jacob Zuma, requesting that he establish a Judicial Commission of Inquiry in terms of section 84(2)(f) of the Constitution, to rigorously investigate what exactly transpired, how it was allowed to transpire, what national governments role was – and ought to have been, and to identify the shortcoming of the current system so as to avoid a catastrophe like this from occurring again," said Maimane.
He said the terms of reference of the Commission ought to be wide, so as to include an investigation into the treatment of mental health patients across the country.
"The Esidimeni tragedy will forever be remembered as one of the most horrendous and systematic failures of government to protect the most vulnerable members in our society. A shameful violation of fundamental human rights by an uncaring and indifferent ANC government."