The governor is accused of irregularly awarding a tender worth Sh382 million and approving Sh18 million in unauthorised payments to himself.
The allegations have raised fresh concerns about the use of public funds in the county government and sparked public debate on accountability among senior leaders.
According to investigators, the Sh382 million tender was allegedly awarded without following proper procurement procedures.
It is claimed that key legal requirements were ignored, raising questions about transparency, fairness, and value for money.
Officials probing the matter say such actions, if proven, amount to abuse of office and misuse of public resources.
In addition to the tender claims, Governor Nyaribo is also accused of receiving Sh18 million through payments that were not approved under existing government rules.
Investigators say the payments were irregular and lacked proper authorization, prompting suspicions that public money may have been diverted for personal benefit.
During questioning, the governor was grilled on how the tender was issued and the circumstances under which the payments were made.
He was asked to provide documents and explanations to justify the decisions taken by his administration.
Sources familiar with the probe said investigators were keen to establish whether due process was followed or deliberately ignored.
Governor Nyaribo has denied any wrongdoing, maintaining that all decisions made by his administration were lawful and in line with county regulations.
He has insisted that the allegations are politically motivated and meant to tarnish his name.
The governor said he is ready to cooperate fully with investigators to clear his name.