The impersonator was discovered after he was found writing the name of the candidate, who was also sitting the examination in the same room.
The imposter and the candidate left the space for filling their names blank only to fill at the end of the exam.
The university student was Index 10 while the candidate he was trying to assist was Index 11.
Kisii county police commander Edward Muli said the suspect will be arraigned immediately investigations are complete.
“Investigations are ongoing and the suspect is expected to be arraigned in court soon,” Muli said.
Read: Alarm as Kitui reports 110 pregnancy cases during KCSE exams
“Those who are trying to engage in examination malpractices should be warned that they will not evade the trap.”
His arrest comes four days after 15 people including the principal of Monianku Secondary School in South Mugirango were arrested and arraigned in Ogembo and charged with being in possession of examination papers and abetting access to examination materials.
The 15 did not take plea after the prosecution urged the court to direct that they be remanded at Nyamarambe police station to enable investigators conclude probe.
Area senior resident magistrate Margaret Nafula set November 12 for the mention of the case.
This year’s Kenya Certificate of Secondary Education exam started last week amid tight security and new directives to curb cheating.
The 664,585 candidates started with a mathematics paper in the morning before tackling chemistry in the afternoon.
The test is being done across 10,077 centres. Education CS Amina Mohamed directed documentation of each process from collection of papers to when they are returned to the safety container at subcounty headquarters.
The documentation will be filed as a report and forwarded to a ministry official stationed at the headquarters at the Kenya National Examinations Council.
Read: Amina orders probe after over 20 girls give birth during KCPE exams
Centre managers are required to indicate the number of extra scripts issued during collection of the papers and the time papers are collected.
“This will provide data that can be used to verify any issues of shortage or missing scripts,” Amina’s directive says.
The CS is the only person authorised to give a go-ahead on duplication of any exam material. Invigilators, supervisors or principals are not allowed to photocopy the exam papers.
Knec also warned against purchase and circulation of fake exam papers
Knec chairman George Magoha asked officials to pay special attention on early exposure of the exams and communication within and outside the centres. Directives to ensure early exposure is avoided include strict timelines on opening of the exam papers and stoppage time.