Kariuki was shot on the left side of face and was rushed to the Bliss health facility along Moi Avenue by well-wishers, where first aid was administered.
He was then transferred to the Kenyatta National Hospital, where he succumbed after two surgeries on his brain to save his life.
"You will not plead to the charge today," Justice Kimondo told Masinde.
"You will be removed from police custody and you will be remanded at Nairobi Remand. You shall be escorted to Mbagathi District Hospital or Kenyatta National Hospital, or indeed any other convenient government facility for mental assessment. Plea is accordingly deferred to July 28, 2025."
The judge, however, informed Masinde that he is charged with murder contrary to Section 203 as read with Section 204 of the Penal Code.
"The particulars of the charge indicate that on June 17, 2025, outside Imenti House in Nairobi's Central Business District, within Nairobi County, you murdered Boniface Kariuki Mwangi," the judge said.
"The High Court has received information dated July 9, 2025, under the hand of Gikui Gichuhi, Senior Assistant Director of Public Prosecutions, charging you with murder...
"However, for the time being, you need not comment on that information or plead to that charge until you are examined by a consultant psychiatrist as to your mental capacity to follow these proceedings or to plead to the information and charge."
Justice Kimondo scheduled Masinde's plea-taking for July 28, 2025, at 11:00 a.m. in open court.
Masinde was arraigned before the High Court after the Office of the Director of Public Prosecutions (ODPP) approved murder charges following investigations into the shooting incident.
This was moments after a Milimani lower court had released the second suspect, Kiprono, and closed the miscellaneous application against him after the ODPP stated they would not be charging him with murder.
The ODPP dropped murder charges against Officer Kiprono, citing a lack of evidence linking him to the murder of Kariuki.
The prosecution, however, did not make it clear whether he would be treated as a witness in the case against Masinde or face assault charges.
Consequently, trial magistrate Benmark Ekhubi ruled that there were insufficient grounds to continue detaining Kiprono in connection with Kariuki's killing.
Magistrate Ekhubi, however, allowed the prosecution to proceed with murder charges against Masinde, who is alleged to be the officer caught on camera firing the fatal shot that killed Kariuki
Kariuki's killing attracted condemnation of police excesses.
Law Society of Kenya president Faith Odhiambo, in reaction to the incident, said the officer should be treated as the face of impunity and criminality at National Police Service
She said the shooting was not only unjustified but premeditated as well, and adds to the complaints against police disregarding human life, despite Kariuki not being involved in the demos.
"Their punishment must serve as a lasting deterrent for all officers who undermine and violate their constitutional duties," she added.
Kariuki died on June 30, 2025 at 3.15 pm after being on life support machine for nearly two weeks.